Theabovequotationssumupprettywellthestatementsofallpreviouswriters。Furthermore，therearesomewritersonNaturalHistorywhohavenotventuredtolaydownthelawinsuchprecisetermsasregardstheveins，butwhoallalikeagreeinassigningtheheadandthebrainasthestarting-pointoftheveins。Andinthisopiniontheyaremistaken。
Theinvestigationofsuchasubject，ashasbeenremarked，isonefraughtwithdifficulties；but，ifanyonebekeenlyinterestedinthematter，hisbestplanwillbetoallowhisanimalstostarvetoemaciation，thentostranglethemonasudden，andthereupontoprosecutehisinvestigations。
Wenowproceedtogiveparticularsregardingthepropertiesandfunctionsoftheveins。Therearetwoblood-vesselsinthethoraxbythebackbone，andlyingtoitsinnerside；andofthesetwothelargeroneissituatedtothefront，andthelesseroneistotherearofit；
andthelargerissituatedrathertotherighthandsideofthebody，andthelesseronetotheleft；andbysomethisveinistermedthe\'aorta\'，fromthefactthatevenindeadbodiespartofitisobservedtobefullofair。Theseblood-vesselshavetheiroriginsintheheart，fortheytraversetheotherviscera，inwhateverdirectiontheyhappentorun，withoutinanywaylosingtheirdistinctivecharacteristicasblood-vessels，whereastheheartisasitwereapartofthemandthattoomoreinrespecttothefrontwardandlargeroneofthetwo，owingtothefactthatthesetwoveinsareaboveandbelow，withtheheartlyingmidway。
Theheartinallanimalshascavitiesinsideit。Inthecaseofthesmalleranimalseventhelargestofthechambersisscarcelydiscernible；thesecondlargerisscarcelydiscernibleinanimalsofmediumsize；butinthelargestanimalsallthreechambersaredistinctlyseen。Intheheartthenwithitspointedenddirectedfrontwards，ashasbeenobservedthelargestofthethreechambersisontheright-handsideandhighestup；theleastoneisontheleft-handside；andthemedium-sizedoneliesinbetwixttheothertwo；andthelargestoneofthethreechambersisagreatdeallargerthaneitherofthetwoothers。Allthree，however，areconnectedwithpassagesleadinginthedirectionofthelung，butallthesecommunicationsareindistinctlydiscerniblebyreasonoftheirminuteness，exceptone。
Thegreatblood-vessel，then，isattachedtothebiggestofthethreechambers，theonethatliesuppermostandontheright-handside；itthenextendsrightthroughthechamber，comingoutasblood-vesselagain；justasthoughthecavityoftheheartwereapartofthevessel，inwhichthebloodbroadensitschannelasariverthatwidensoutinalake。Theaortaisattachedtothemiddlechamber；
only，bytheway，itisconnectedwithitbymuchnarrowerpipe。
Thegreatblood-vesselthenpassesthroughtheheartandrunsfromtheheartintotheaorta。Thegreatvessellooksasthoughmadeofmembraneorskin，whiletheaortaisnarrowerthanit，andisverysinewy；andasitstretchesawaytotheheadandtothelowerpartsitbecomesexceedinglynarrowandsinewy。
Firstofall，then，upwardsfromthehearttherestretchesapartofthegreatblood-vesseltowardsthelungandtheattachmentoftheaorta，apartconsistingofalargeundividedvessel。Buttheresplitofffromittwoparts；onetowardsthelungandtheothertowardsthebackboneandthelastvertebraoftheneck。
Thevessel，then，thatextendstothelung，asthelungitselfisduplicate，dividesatfirstintotwo；andthenextendsalongbyeverypipeandeveryperforation，greateralongthegreaterones，lesseralongtheless，socontinuouslythatitisimpossibletodiscernasinglepartwhereinthereisnotperforationandvein；fortheextremitiesareindistinguishablefromtheirminuteness，andinpointoffactthewholelungappearstobefilledwithblood。
Thebranchesoftheblood-vesselslieabovethetubesthatextendfromthewindpipe。Andthatvesselwhichextendstothevertebraoftheneckandthebackbone，stretchesbackagainalongthebackbone；asHomerrepresentsinthelines:-
Antilochus，asThoonturnedhimround，Transpierc\'dhisbackwithadishonestwound；
Thehollowveinthattotheneckextends，Alongthechine，theeagerjavelinrends。
Fromthisvesselthereextendsmallblood-vesselsateachribandeachvertebra；andatthevertebraabovethekidneysthevesselbifurcates。Andintheabovewaythepartsbranchofffromthegreatblood-vessel。
Butupaboveallthese，fromthatpartwhichisconnectedwiththeheart，theentireveinbranchesoffintwodirections。Foritsbranchesextendtothesidesandtothecollarbones，andthenpasson，inmenthroughthearmpitstothearms，inquadrupedstotheforelegs，inbirdstothewings，andinfishestotheupperorpectoralfins。
Seediagram。Thetrunksoftheseveins，wheretheyfirstbranchoff，arecalledthe\'jugular\'veins；and，wheretheybranchofftotheneckthegreatveinrunalongsidethewindpipe；and，occasionally，iftheseveinsarepressedexternally，men，thoughnotactuallychoked，becomeinsensible，shuttheireyes，andfallflatontheground。Extendinginthewaydescribedandkeepingthewindpipeinbetwixtthem，theypassonuntiltheyreachtheearsatthejunctionofthelowerjawwiththeskull。Henceagaintheybranchoffintofourveins，ofwhichonebendsbackanddescendsthroughtheneckandtheshoulder，andmeetsthepreviousbranchingoffoftheveinatthebendofthearm，whiletherestofitterminatesatthehandandfingers。Seediagram。
Eachveinoftheotherpairstretchesfromtheregionoftheeartothebrain，andbranchesoffinanumberoffineanddelicateveinsintotheso-calledmeninx，ormembrane，whichsurroundsthebrain。Thebrainitselfinallanimalsisdestituteofblood，andnovein，greatorsmall，holdsitscoursetherein。Butoftheremainingveinsthatbranchofffromthelastmentionedveinsomeenvelopthehead，othersclosetheircoursesintheorgansofsenseandattherootsoftheteethinveinsexceedinglyfineandminute。
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Andinlikemannerthepartsofthelesseroneofthetwochiefblood-vessels，designatedtheaorta，branchoff，accompanyingthebranchesfromthebigvein；onlythat，inregardtotheaorta，thepassagesarelessinsize，andthebranchesveryconsiderablylessthanarethoseofthegreatvein。Somuchfortheveinsasobservedintheregionsabovetheheart。
Thepartofthegreatveinthatliesunderneaththeheartextends，freelysuspended，rightthroughthemidriff，andisunitedbothtotheaortaandthebackbonebyslackmembranouscommunications。
Fromitonevein，shortandwide，extendsthroughtheliver，andfromitanumberofminuteveinsbranchoffintotheliveranddisappear。Fromtheveinthatpassesthroughthelivertwobranchesseparateoff，ofwhichoneterminatesinthediaphragmorso-calledmidriff，andtheotherrunsupagainthroughthearmpitintotherightarmanduniteswiththeotherveinsattheinsideofthebendofthearm；anditisinconsequenceofthislocalconnexionthat，whenthesurgeonopensthisveinintheforearm，thepatientisrelievedofcertainpainsintheliver；andfromtheleft-handsideofitthereextendsashortbutthickveintothespleenandthelittleveinsbranchingoffitdisappearinthatorgan。Anotherpartbranchesofffromtheleft-handsideofthegreatvein，andascends，byacoursesimilartothecourserecentlydescribed，intotheleftarm；onlythattheascendingveinintheonecaseistheveinthattraversestheliver，whileinthiscaseitisdistinctfromtheveinthatrunsintothespleen。Again，otherveinsbranchofffromthebigvein；
onetotheomentum，andanothertothepancreas，fromwhichveinrunanumberofveinsthroughthemesentery。Alltheseveinscoalesceinasinglelargevein，alongtheentiregutandstomachtotheoesophagus；
aboutthesepartsthereisagreatramificationofbranchveins。
Asfarasthekidneys，eachofthetworemainingundivided，theaortaandthebigveinextend；andheretheygetmorecloselyattachedtothebackbone，andbranchoff，eachofthetwo，intoaAshape，andthebigveingetstotherearoftheaorta。Butthechiefattachmentoftheaortatothebackbonetakesplaceintheregionoftheheart；andtheattachmentiseffectedbymeansofminuteandsinewyvessels。Theaorta，justasitdrawsofffromtheheart，isatubeofconsiderablevolume，but，asitadvancesinitscourse，itgetsnarrowerandmoresinewy。Andfromtheaortathereextendveinstothemesenteryjustliketheveinsthatextendthitherfromthebigvein，onlythatthebranchesinthecaseoftheaortaareconsiderablylessinmagnitude；theyare，indeed，narrowandfibrillar，andtheyendindelicatehollowfibre-likeveinlets。
Thereisnovesselthatrunsfromtheaortaintotheliverorthespleen。
Fromeachofthetwogreatblood-vesselsthereextendbranchestoeachofthetwoflanks，andbothbranchesfastenontothebone。
Vesselsalsoextendtothekidneysfromthebigveinandtheaorta；
onlythattheydonotopenintothecavityoftheorgan，buttheirramificationspenetrateintoitssubstance。Fromtheaortaruntwootherductstothebladder，firmandcontinuous；andthereareotherductsfromthehollowofthekidneys，innowaycommunicatingwiththebigvein。Fromthecentreofeachofthetwokidneysspringsahollowsinewyvein，runningalongthebackbonerightthroughtheloins；byandbyeachofthetwoveinsfirstdisappearsinitsownflank，andsoonafterwardsreappearsstretchinginthedirectionoftheflank。Theextremitiesoftheseattachtothebladder，andalsointhemaletothepenisandinthefemaletothewomb。Fromthebigveinnoveinextendstothewomb，buttheorganisconnectedwiththeaortabyveinsnumerousandcloselypacked。
Furthermore，fromtheaortaandthegreatveinatthepointsofdivaricationtherebranchoffotherveins。Someoftheseruntothegroins-largehollowveins-andthenpassondownthroughthelegsandterminateinthefeetandtoes。And，again，anothersetrunthroughthegroinsandthethighscross-garterfashion，fromrighttoleftandfromlefttoright，anduniteinthehamswiththeotherveins。
Intheabovedescriptionwehavethrownlightuponthecourseoftheveinsandtheirpointsofdeparture。
Inallsanguineousanimalsthecasestandsasheresetforthinregardtothepointsofdepartureandthecoursesofthechiefveins。Butthedescriptiondoesnotholdequallygoodfortheentirevein-systeminalltheseanimals。For，inpointoffact，theorgansarenotidenticallysituatedinthemall；and，whatismore，someanimalsarefurnishedwithorgansofwhichotheranimalsaredestitute。Atthesametime，whilethedescriptionsofarholdsgood，theproofofitsaccuracyisnotequallyeasyinallcases，butiseasiestinthecaseofanimalsofconsiderablemagnitudeandsuppliedabundantlywithblood。Forinlittleanimalsandthosescantilysuppliedwithblood，eitherfromnaturalandinherentcausesorfromaprevalenceoffatinthebody，thoroughaccuracyininvestigationisnotequallyattainable；forinthelatterofthesecreaturesthepassagesgetclogged，likewater-channelschokedwithslush；andtheothershaveafewminutefibrestoserveinsteadofveins。Butinallcasesthebigveinisplainlydiscernible，evenincreaturesofinsignificantsize。
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Thesinewsofanimalshavethefollowingproperties。Forthesealsothepointoforiginistheheart；forthehearthassinewswithinitselfinthelargestofitsthreechambers，andtheaortaisasinew-likevein；infact，atitsextremityitisactuallyasinew，foritistherenolongerhollow，andisstretchedlikethesinewswheretheyterminateatthejointingsofthebones。Beitremembered，however，thatthesinewsdonotproceedinunbrokensequencefromonepointoforigin，asdotheblood-vessels。
Fortheveinshavetheshapeoftheentirebody，likeasketchofamannikin；insuchawaythatthewholeframeseemstobefilledupwithlittleveinsinattenuatedsubjects-forthespaceoccupiedbyfleshinfatindividualsisfilledwithlittleveinsinthinones-whereasthesinewsaredistributedaboutthejointsandtheflexuresofthebones。Now，ifthesinewswerederivedinunbrokensequencefromacommonpointofdeparture，thiscontinuitywouldbediscernibleinattenuatedspecimens。
Intheham，orthepartoftheframebroughtintofullplayintheeffortofleaping，isanimportantsystemofsinews；andanothersinew，adoubleone，isthatcalled\'thetendon\'，andothersarethosebroughtintoplaywhenagreateffortofphysicalstrengthisrequired；thatistosay，theepitonosorback-stayandtheshoulder-sinews。Othersinews，devoidofspecificdesignation，aresituatedintheregionoftheflexuresofthebones；forallthebonesthatareattachedtooneanotherareboundtogetherbysinews，andagreatquantityofsinewsareplacedintheneighbourhoodofallthebones。Only，bytheway，intheheadthereisnosinew；buttheheadisheldtogetherbythesuturesofthebones。
Sinewisfissilelengthwise，butcrosswiseitisnoteasilybroken，butadmitsofaconsiderableamountofhardtension。Inconnexionwithsinewsaliquidmucusisdeveloped，whiteandglutinous，andtheorgan，infact，issustainedbyitandappearstobesubstantiallycomposedofit。Now，veinmaybesubmittedtotheactualcautery，butsinew，whensubmittedtosuchaction，shrivelsupaltogether；and，ifsinewsbecutasunder，theseveredpartswillnotagaincohere。Afeelingofnumbnessisincidentalonlytopartsoftheframewheresinewissituated。
Thereisaveryextensivesystemofsinewsconnectedseverallywiththefeet，thehands，theribs，theshoulder-blades，theneck，andthearms。
Allanimalssuppliedwithbloodarefurnishedwithsinews；butinthecaseofanimalsthathavenoflexurestotheirlimbs，butare，infact，destituteofeitherfeetorhands，thesinewsarefineandinconspicuous；andso，asmighthavebeenanticipated，thesinewsinthefisharechieflydiscernibleinconnexionwiththefin。
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Theinesorfibrousconnectivetissueareasomethingintermediatebetweensinewandvein。Someofthemaresuppliedwithfluid，thelymph；andtheypassfromsinewtoveinandfromveintosinew。Thereisanotherkindofinesorfibrethatisfoundinblood，butnotinthebloodofallanimalsalike。Ifthisfibrebeleftintheblood，thebloodwillcoagulate；ifitberemovedorextracted，thebloodisfoundtobeincapableofcoagulation。While，however，thisfibrousmatterisfoundinthebloodofthegreatmajorityofanimals，itisnotfoundinall。Forinstance，wefailtofinditinthebloodofthedeer，theroe，theantelope，andsomeotheranimals；and，owingtothisdeficiencyofthefibroustissue，thebloodoftheseanimalsdoesnotcoagulatetotheextentobservedinthebloodofotheranimals。Thebloodofthedeercoagulatestoaboutthesameextentasthatofthehare:thatistothebloodineithercasecoagulates，butnotintoastifforjelly-likesubstance，likethebloodofordinaryanimals，butonlyintoaflaccidconsistencylikethatofmilkwhichisnotsubjectedtotheactionofrennet。Thebloodoftheantelopeadmitsofafirmerconsistencyincoagulation；forinthisrespectitresembles，oronlycomesalittleshortof，thebloodofsheep。Sucharethepropertiesofvein，sinew，andfibroustissue。
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Thebonesinanimalsareallconnectedwithonesinglebone，andareinterconnected，liketheveins，inoneunbrokensequence；andthereisnoinstanceofabonestandingapartbyitself。Inallanimalsfurnishedwithbones，thespineorbackboneisthepointoforiginfortheentireosseoussystem。Thespineiscomposedofvertebrae，anditextendsfromtheheaddowntotheloins。Thevertebraeareallperforated，and，above，thebonyportionoftheheadisconnectedwiththetopmostvertebrae，andisdesignatedthe\'skull\'。Andtheserratedlinesontheskullaretermed\'sutures\'。
Theskullisnotformedalikeinallanimals。Insomeanimalstheskullconsistsofonesingleundividedbone，asinthecaseofthedog；inothersitiscompositeinstructure，asinman；andinthehumanspeciesthesutureiscircularinthefemale，whileinthemaleitismadeupofthreeseparatesutures，unitingaboveinthree-cornerfashion；andinstanceshavebeenknownofaman\'sskullbeingdevoidofsuturealtogether。Theskulliscomposednotoffourbones，butofsix；twooftheseareintheregionoftheears，smallincomparisonwiththeotherfour。Fromtheskullextendthejaws，constitutedofbone。Animalsingeneralmovethelowerjaw；therivercrocodileistheonlyanimalthatmovestheupperone。Inthejawsisthetooth-system；andtheteethareconstitutedofbone，andarehalf-wayperforated；andtheboneinquestionistheonlykindofbonewhichitisfoundimpossibletogravewithagravingtool。
Ontheupperpartofthecourseofthebackbonearethecollar-bonesandtheribs。Thechestrestsonribs；andtheseribsmeettogether，whereastheothersdonot；fornoanimalhasboneintheregionofthestomach。Thencometheshoulder-bones，orblade-bones，andthearm-bonesconnectedwiththese，andthebonesinthehandsconnectedwiththebonesofthearms。Withanimalsthathaveforelegs，theosseoussystemoftheforelegresemblesthatofthearminman。
Belowthelevelofthebackbone，afterthehaunch-bone，comesthehip-socket；thentheleg-bones，thoseinthethighsandthoseintheshins，whicharetermedcolenesorlimb-bones，apartofwhichistheankle，whileapartofthesameistheso-called\'plectrum\'
inthosecreaturesthathaveanankle；andconnectedwiththesebonesarethebonesinthefeet。
Now，withallanimalsthataresuppliedwithbloodandfurnishedwithfeet，andareatthesametimeviviparous，thebonesdonotdiffergreatlyonefromanother，butonlyinthewayofrelativehardness，softness，ormagnitude。Afurtherdifference，bytheway，isthatinoneandthesameanimalcertainbonesaresuppliedwithmarrow，whileothersaredestituteofit。Someanimalsmightoncasualobservationappeartohavenomarrowwhatsoeverintheirbones:asisthecasewiththelion，owingtohishavingmarrowonlyinsmallamount，poorandthin，andinveryfewbones；formarrowisfoundinhisthighandarmbones。Thebonesofthelionareexceptionallyhard；sohard，infact，thatiftheyarerubbedhardagainstoneanothertheyemitsparkslikeflint-stones。Thedolphinhasbones，andnotfish-spine。
Oftheotheranimalssuppliedwithblood，somedifferbutlittle，asisthecasewithbirds；othershavesystemsanalogous，asfishes；forviviparousfishes，suchasthecartilaginousspecies，aregristle-spined，whiletheoviparahaveaspinewhichcorrespondstothebackboneinquadrupeds。Thisexceptionalpropertyhasbeenobservedinfishes，thatinsomeofthemtherearefounddelicatespinesscatteredhereandtherethroughoutthefleshyparts。Theserpentissimilarlyconstructedtothefish；inotherwords，hisbackboneisspinous。Withoviparousquadrupeds，theskeletonofthelargeronesismoreorlessosseous；ofthesmallerones，moreorlessspinous。Butallsanguineousanimalshaveabackboneofeitheronekindorother:thatis，composedeitherofboneorofspine。
Theotherportionsoftheskeletonarefoundinsomeanimalsandnotfoundinothers，butthepresenceortheabsenceofthisandthatpartcarrieswithit，asamatterofcourse，thepresenceortheabsenceofthebonesorthespinescorrespondingtothisorthatpart。Foranimalsthataredestituteofarmsandlegscannotbefurnishedwithlimb-bones:andinlikemannerwithanimalsthathavethesameparts，butyethavethemunlikeinform；forintheseanimalsthecorrespondingbonesdifferfromoneanotherinthewayofrelativeexcessorrelativedefect，orinthewayofanalogytakingtheplaceofidentity。Somuchfortheosseousorspinoussystemsinanimals。
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Gristleisofthesamenatureasbone，butdiffersfromitinthewayofrelativeexcessorrelativedefect。Andjustlikebone，cartilagealso，ifcut，doesnotgrowagain。Interrestrialviviparoussanguineathegristleformationsareunperforated，andthereisnomarrowinthemasthereisinbones；intheselachia，however——for，beitobserved，theyaregristle-spined——thereisfoundinthecaseoftheflatspaceintheregionofthebackbone，agristle-likesubstanceanalogoustobone，andinthisgristle-likesubstancethereisaliquidresemblingmarrow。Inviviparousanimalsfurnishedwithfeet，gristleformationsarefoundintheregionoftheears，inthenostrils，andaroundcertainextremitiesofthebones。
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Furthermore，therearepartsofotherkinds，neitheridenticalwith，noraltogetherdiversefrom，thepartsaboveenumerated:suchasnails，hooves，claws，andhorns；andalso，bytheway，beaks，suchasbirdsarefurnishedwith-allintheseveralanimalsthatarefurnishedtherewithal。Allthesepartsareflexibleandfissile；butboneisneitherflexiblenorfissile，butfrangible。
Andthecoloursofhornsandnailsandclawandhooffollowthecolouroftheskinandthehair。Foraccordingastheskinofananimalisblack，orwhite，orofmediumhue，soarethehorns，theclaws，orthehooves，asthecasemaybe，ofhuetomatch。Anditisthesamewithnails。Theteeth，however，followafterthebones。
Thusinblackmen，suchastheAethiopiansandthelike，theteethandbonesarewhite，butthenailsareblack，likethewholeoftheskin。
Hornsingeneralarehollowattheirpointofattachmenttothebonewhichjutsoutfromtheheadinsidethehorn，buttheyhaveasolidportionatthetip，andtheyaresimpleandundividedinstructure。Inthecaseofthestagaloneofallanimalsthehornsaresolidthroughout，andramifyintobranchesorantlers。And，whereasnootheranimalisknowntosheditshorns，thedeershedsitshornsannually，unlessithasbeencastrated；andwithregardtotheeffectsofcastrationinanimalsweshallhavemuchtosayhereafter。Hornsattachrathertotheskinthantothebone；whichwillaccountforthefactthattherearefoundinPhrygiaandelsewherecattlethatcanmovetheirhornsasfreelyastheirears。
Ofanimalsfurnishedwithnails-and，bytheway，allanimalshavenailsthathavetoes，andtoesthathavefeet，excepttheelephant；andtheelephanthastoesundividedandslightlyarticulated，buthasnonailswhatsoever——ofanimalsfurnishedwithnails，somearestraight-nailed，likeman；othersarecrookednailed，asthelionamonganimalsthatwalk，andtheeagleamonganimalsthatfly。
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Thefollowingarethepropertiesofhairandofpartsanalogoustohair，andofskinorhide。Allviviparousanimalsfurnishedwithfeethavehair；alloviparousanimalsfurnishedwithfeethavehorn-liketessellates；fishes，andfishesonly，havescales-thatis，suchoviparousfishesashavethecrumblingeggorroe。Forofthelankyfishes，thecongerhasnosuchegg，northemuraena，andtheeelhasnoeggatall。
Thehairdiffersinthewayofthicknessandfineness，andoflength，accordingtothelocalityofthepartinwhichitisfound，andaccordingtothequalityofskinorhideonwhichitgrows。For，asageneralrule，thethickerthehide，theharderandthethickeristhehair；andthehairisinclinedtogrowinabundanceandtoagreatlengthinlocalitiesofthebodieshollowandmoist，ifthelocalitiesbefittedforthegrowthofhairatall。Thefactsaresimilarinthecaseofanimalswhethercoatedwithscalesorwithtessellates。
Withsoft-hairedanimalsthehairgetsharderwithgoodfeeding，andwithhard-hairedorbristlyanimalsitgetssofterandscantierfromthesamecause。Hairdiffersinqualityalsoaccordingtotherelativeheatorwarmthofthelocality:justasthehairinmanishardinwarmplacesandsoftincoldones。Again，straighthairisinclinedtobesoft，andcurlyhairtobebristly。
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Hairisnaturallyfissile，andinthisrespectitdiffersindegreeindiverseanimals。Insomeanimalsthehairgoesongraduallyhardeningintobristleuntilitnolongerresembleshairbutspine，asinthecaseofthehedgehog。Andinlikemannerwiththenails；forinsomeanimalsthenaildiffersasregardssolidityinnowayfrombone。
Ofallanimalsmanhasthemostdelicateskin:thatis，ifwetakeintoconsiderationhisrelativesize。Intheskinorhideofallanimalsthereisamucousliquid，scantyinsomeanimalsandplentifulinothers，as，forinstance，inthehideoftheox；formenmanufactureglueoutofit。And，bytheway，insomecasesglueismanufacturedfromfishesalso。Theskin，whencut，isinitselfdevoidofsensation；andthisisespeciallythecasewiththeskinonthehead，owingtotherebeingnofleshbetweenitandtheskull。
Andwherevertheskinisquitebyitself，ifitbecutasunder，itdoesnotgrowtogetheragain，asisseeninthethinpartofthejaw，intheprepuce，andtheeyelid。Inallanimalstheskinisoneofthepartsthatextendscontinuousandunbroken，anditcomestoastoponlywherethenaturalductspourouttheircontents，andatthemouthandnails。
Allsanguineousanimals，then，haveskin；butnotallsuchanimalshavehair，saveonlyunderthecircumstancesdescribedabove。Thehairchangesitscolourasanimalsgrowold，andinmanitturnswhiteorgrey。Withanimals，ingeneral，thechangetakesplace，butnotveryobviously，ornotsoobviouslyasinthecaseofthehorse。Hairturnsgreyfromthepointbackwardstotheroots。But，inthemajorityofcases，greyhairsarewhitefromthebeginning；andthisisaproofthatgreynessofhairdoesnot，assomebelievetobethecase，implywitheringordecrepitude，fornopartisbroughtintoexistenceinawitheredordecrepitcondition。
Intheeruptivemaladycalledthewhite-sicknessallthehairsgetgrey；andinstanceshavebeenknownwherethehairbecamegreywhilethepatientswereillofthemalady，whereasthegreyhairsshedoffandblackonesreplacedthemontheirrecovery。Hairismoreapttoturngreywhenitiskeptcoveredthanwhenexposedtotheactionoftheouterair。Inmen，thehairoverthetemplesisthefirsttoturngrey，andthehairinthefrontgrowsgreysoonerthanthehairattheback；andthehaironthepubesisthelasttochangecolour。
Somehairsarecongenital，othersgrowafterthematurityoftheanimal；butthisoccursinmanonly。Thecongenitalhairsareonthehead，theeyelids，andtheeyebrows；ofthelatergrowthsthehairsonthepubesarethefirsttocome，thenthoseunderthearmpits，and，thirdly，thoseonthechin；for，singularlyenough，theregionswherecongenitalgrowthsandthesubsequentgrowthsarefoundareequalinnumber。Thehairontheheadgrowsscantyandshedsouttoagreaterextentandsoonerthanalltherest。Butthisremarkappliesonlytohairinfront；fornomanevergetsbaldatthebackofhishead。Smoothnessonthetopoftheheadistermed\'baldness\'，butsmoothnessontheeyebrowsisdenotedbyaspecialtermwhichmeans\'forehead-baldness\'；andneitheroftheseconditionsofbaldnesssupervenesinamanuntilheshallhavecomeundertheinfluenceofsexualpassion。Fornoboyevergetsbald，nowoman，andnocastratedman。Infact，ifamanbecastratedbeforereachingpuberty，thelatergrowthsofhairnevercomeatall；and，iftheoperationtakeplacesubsequently，theaftergrowths，andtheseonly，shedoff；
or，rather，twoofthegrowthsshedoff，butnotthatonthepubes。
Womendonotgrowhairsonthechin；exceptthatascantybeardgrowsonsomewomenafterthemonthlycourseshavestopped；andsimilarphenomenonisobservedattimesinpriestessesinCaria，butthesecasesarelookeduponasportentouswithregardtocomingevents。Theotherafter-growthsarefoundinwomen，butmorescantyandsparse。Menandwomenareattimesbornconstitutionallyandcongenitallyincapableoftheafter-growths；andindividualsthataredestituteevenofthegrowthuponthepubesareconstitutionallyimpotent。
Hairasarulegrowsmoreorlessinlengthasthewearergrowsinage；chieflythehaironthehead，thenthatinthebeard，andfinehairgrowslongestofall。Withsomepeopleastheygrowoldtheeyebrowsgrowthicker，tosuchanextentthattheyhavetobecutoff；
andthisgrowthisowingtothefactthattheeyebrowsaresituatedataconjunctureofbones，andthesebones，asagecomeson，drawapartandexudeagradualincreaseofmoistureorrheum。Theeyelashesdonotgrowinsize，buttheyshedwhenthewearercomesfirstundertheinfluenceofsexualfeelings，andshedallthequickerasthisinfluenceisthemorepowerful；andthesearethelasthairstogrowgrey。
Hairsifpluckedoutbeforematuritygrowagain；buttheydonotgrowagainifpluckedoutafterwards。Everyhairissuppliedwithamucousmoistureatitsroot，andimmediatelyafterbeingpluckedoutitcanliftlightarticlesifittouchthemwiththismucus。
Animalsthatadmitofdiversityofcolourinthehairadmitofasimilardiversitytostartwithintheskinandinthecuticleofthetongue。
Insomecasesamongmentheupperlipandthechinisthicklycoveredwithhair，andinothercasesthesepartsaresmoothandthecheeksarehairy；and，bytheway，smooth-chinnedmenarelessinclinedthanbeardedmentobaldness。
Thehairisinclinedtogrowincertaindiseases，especiallyinconsumption，andinoldage，andafterdeath；andunderthesecircumstancesthehairhardensconcomitantlywithitsgrowth，andthesameduplicatephenomenonisobservableinrespectofthenails。
Inthecaseofmenofstrongsexualpassionsthecongenitalhairsshedthesooner，whilethehairsoftheafter-growthsarethequickertocome。Whenmenareafflictedwithvaricoseveinstheyarelessinclinedtotakeonbaldness；andiftheybebaldwhentheybecomethusafflicted，theyhaveatendencytogettheirhairagain。
Ifahairbecut，itdoesnotgrowatthepointofsection；butitgetslongerbygrowingupwardfrombelow。Infishesthescalesgrowharderandthickerwithage，andwhentheamimalgetsemaciatedorisgrowingoldthescalesgrowharder。Inquadrupedsastheygrowoldthehairinsomeandthewoolinothersgetsdeeperbutscantierinamount:andthehoovesorclawsgetlargerinsize；andthesameisthecasewiththebeaksofbirds。Theclawsalsoincreaseinsize，asdoalsothenails。
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Withregardtowingedanimals，suchasbirds，nocreatureisliabletochangeofcolourbyreasonofage，exceptingthecrane。
Thewingsofthisbirdareash-colouredatfirst，butasitgrowsoldthewingsgetblack。Again，owingtospecialclimaticinfluences，aswhenunusualfrostprevails，achangeissometimesobservedtotakeplaceinbirdswhoseplumageisofoneuniformcolour；thus，birdsthathaveduskyordownrightblackplumageturnwhiteorgrey，astheraven，thesparrow，andtheswallow；butnocasehaseveryetbeenknownofachangeofcolourfromwhitetoblack。
Further，mostbirdschangethecolouroftheirplumageatdifferentseasonsoftheyear，somuchsothatamanignorantoftheirhabitsmightbemistakenastotheiridentity。Someanimalschangethecolouroftheirhairwithachangeintheirdrinking-water，forinsomecountriesthesamespeciesofanimalisfoundwhiteinonedistrictandblackinanother。Andinregardtothecommerceofthesexes，waterinmanyplacesisofsuchpeculiarqualitythatrams，iftheyhaveintercoursewiththefemaleafterdrinkingit，begetblacklambs，asisthecasewiththewaterofthePsychrusso-calledfromitscoldness，ariverinthedistrictofAssyritisintheChalcidicPeninsula，onthecoastofThrace；andinAntandriatherearetworiversofwhichonemakesthelambswhiteandtheotherblack。TheriverScamanderalsohasthereputationofmakinglambsyellow，andthatisthereason，theysay，whyHomerdesignatesitthe\'YellowRiver。\'Animalsasageneralrulehavenohairontheirinternalsurfaces，and，inregardtotheirextremities，theyhavehairontheupper，butnotonthelowerside。
Thehare，ordasypod，istheonlyanimalknowntohavehairinsideitsmouthandunderneathitsfeet。Further，theso-calledmousewhaleinsteadofteethhashairsinitsmouthresemblingpigs\'bristles。
Hairsafterbeingcutgrowatthebottombutnotatthetop；iffeathersbecutoff，theygrowneitherattopnorbottom，butshedandfallout。Further，thebee\'swingwillnotgrowagainafterbeingpluckedoff，norwillthewingofanycreaturethathasundividedwings。Neitherwillthestinggrowagainifthebeeloseit，butthecreaturewilldieoftheloss。
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Inallsanguineousanimalsmembranesarefound。Andmembraneresemblesathinclose-texturedskin，butitsqualitiesaredifferent，asitadmitsneitherofcleavagenorofextension。Membraneenvelopseachoneofthebonesandeachoneoftheviscera，bothinthelargerandthesmalleranimals；thoughinthesmalleranimalsthemembranesareindiscerniblefromtheirextremetenuityandminuteness。
Thelargestofallthemembranesarethetwothatsurroundthebrain，andofthesetwotheonethatlinesthebonyskullisstrongerandthickerthantheonethatenvelopsthebrain；nextinorderofmagnitudecomesthemembranethatenclosestheheart。Ifmembranebebaredandcutasunderitwillnotgrowtogetheragain，andthebonethusstrippedofitsmembranemortifies。
14
Theomentumorcaul，bytheway，ismembrane。Allsanguineousanimalsarefurnishedwiththisorgan；butinsomeanimalstheorganissuppliedwithfat，andinothersitisdevoidofit。Theomentumhasbothitsstarting-pointanditsattachment，withambidentalvivipara，inthecentreofthestomach，wherethestomachhasakindofsuture；innon-ambidentalviviparaithasitsstarting-pointandattachmentinthechiefoftheruminatingstomachs。
15
Thebladderalsoisofthenatureofmembrane，butofmembranepeculiarinkind，foritisextensile。Theorganisnotcommontoallanimals，but，whileitisfoundinallthevivipara，thetortoiseistheonlyoviparousanimalthatisfurnishedtherewithal。
Thebladder，likeordinarymembrane，ifcutasunderwillnotgrowtogetheragain，unlessthesectionbejustatthecommencementoftheurethra:exceptindeedinveryrarecases，forinstancesofhealinghavebeenknowntooccur。Afterdeath，theorganpassesnoliquidexcretion；butinlife，inadditiontothenormalliquidexcretion，itpassesattimesdryexcretionalso，whichturnsintostonesinthecaseofsufferersfromthatmalady。Indeed，instanceshavebeenknownofconcretionsinthebladdersoshapedascloselytoresemblecockleshells。
Sucharetheproperties，then，ofvein，sinewandskin，offibreandmembrane，ofhair，nail，clawandhoof，ofhorns，ofteeth，ofbeak，ofgristle，ofbones，andofpartsthatareanalogoustoanyofthepartshereenumerated。
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Flesh，andthatwhichisbynatureakintoitinsanguineousanimals，isinallcasessituatedinbetweentheskinandthebone，orthesubstanceanalogoustobone；forjustasspineisacounterpartofbone，soistheflesh-likesubstanceofanimalsthatareconstructedaspinoussystemthecounterpartofthefleshofanimalsconstructedonanosseousone。
Fleshcanbedividedasunderinanydirection，notlengthwiseonlyasisthecasewithsinewandvein。Whenanimalsaresubjectedtoemaciationthefleshdisappears，andthecreaturesbecomeamassofveinsandfibres；whentheyareoverfed，fattakestheplaceofflesh。Wherethefleshisabundantinananimal，itsveinsaresomewhatsmallandthebloodabnormallyred；thevisceraalsoandthestomacharediminutive；whereaswithanimalswhoseveinsarelargethebloodissomewhatblack，thevisceraandthestomacharelarge，andthefleshissomewhatscanty。Andanimalswithsmallstomachsaredisposedtotakeonflesh。
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Again，fatandsuetdifferfromoneanother。Suetisfrangibleinalldirectionsandcongealsifsubjectedtoextremecold，whereasfatcanmeltbutcannotfreezeorcongeal；andsoupsmadeofthefleshofanimalssuppliedwithfatdonotcongealorcoagulate，asisfoundwithhorse-fleshandpork；butsoupsmadefromthefleshofanimalssuppliedwithsuetdocoagulate，asisseenwithmuttonandgoat\'sflesh。Further，fatandsuetdifferastotheirlocalities:forfatisfoundbetweentheskinandflesh，butsuetisfoundonlyatthelimitofthefleshyparts。Also，inanimalssuppliedwithfattheomentumorcaulissuppliedwithfat，anditissuppliedwithsuetinanimalssuppliedwithsuet。Moreover，ambidentalanimalsaresuppliedwithfat，andnon-ambidentalswithsuet。
Ofthevisceratheliverinsomeanimalsbecomesfatty，as，amongfishes，isthecasewiththeselachia，bythemeltingofwhoseliversanoilismanufactured。Thesecartilaginousfishthemselveshavenofreefatatallinconnexionwiththefleshorwiththestomach。Thesuetinfishisfatty，anddoesnotsolidifyorcongeal。Allanimalsarefurnishedwithfat，eitherintermingledwiththeirflesh，orapart。Suchashavenofreeorseparatefatarelessfatthanothersinstomachandomentum，astheeel；forithasonlyascantysupplyofsuetabouttheomentum。Mostanimalstakeonfatinthebelly，especiallysuchanimalsasarelittleinmotion。
Thebrainsofanimalssuppliedwithfatareoily，asinthepig；
ofanimalssuppliedwithsuet，parchedanddry。Butitisaboutthekidneysmorethananyotherviscerathatanimalsareinclinedtotakeonfat；andtherightkidneyisalwayslesssuppliedwithfatthantheleftkidney，and，bethetwokidneyseversofat，thereisalwaysaspacedevoidoffatinbetweenthetwo。Animalssuppliedwithsuetarespeciallyapttohaveitaboutthekidneys，andespeciallythesheep；forthisanimalisapttodiefromitskidneysbeingentirelyenveloped。Fatorsuetaboutthekidneyissuperinducedbyoverfeeding，asisfoundatLeontiniinSicily；andconsequentlyinthisdistricttheydeferdrivingoutsheeptopastureuntilthedayiswellon，withtheviewoflimitingtheirfoodbycurtailmentofthehoursofpasture。
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Thepartaroundthepupiloftheeyeisfattyinallanimals，andthispartresemblessuetinallanimalsthatpossesssuchapartandthatarenotfurnishedwithhardeyes。
Fatanimals，whethermaleorfemale，aremoreorlessunfittedforbreedingpurposes。Animalsaredisposedtotakeonfatmorewhenoldthanwhenyoung，andespeciallywhentheyhaveattainedtheirfullbreadthandtheirfulllengthandarebeginningtogrowdepthways。
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Andnowtoproceedtotheconsiderationoftheblood。Insanguineousanimalsbloodisthemostuniversalandthemostindispensablepart；anditisnotanacquiredoradventitiouspart，butitisaconsubstantialpartofallanimalsthatarenotcorruptormoribund。Allbloodiscontainedinavascularsystem，towit，theveins，andisfoundnowhereelse，exceptingintheheart。Bloodisnotsensitivetotouchinanyanimal，anymorethantheexcretionsofthestomach；andthecaseissimilarwiththebrainandthemarrow。
Whenfleshislacerated，bloodexudes，iftheanimalbealiveandunlessthefleshbegangrened。Bloodinahealthyconditionisnaturallysweettothetaste，andredincolour，bloodthatdeterioratesfromnaturaldecayorfromdiseasemoreorlessblack。
Bloodatitsbest，beforeitundergoesdeteriorationfromeithernaturaldecayorfromdisease，isneitherverythicknorverythin。Inthelivinganimalitisalwaysliquidandwarm，but，onissuingfromthebody，itcoagulatesinallcasesexceptinthecaseofthedeer，theroe，andthelikeanimals；for，asageneralrule，bloodcoagulatesunlessthefibresbeextracted。Bull\'sbloodisthequickesttocoagulate。
Animalsthatareinternallyandexternallyviviparousaremoreabundantlysuppliedwithbloodthanthesanguineousovipara。Animalsthatareingoodcondition，eitherfromnaturalcausesorfromtheirhealthhavingbeenattendedto，havethebloodneithertooabundant-ascreaturesjustafterdrinkinghavetheliquidinsidetheminabundance-noragainveryscanty，asisthecasewithanimalswhenexceedinglyfat。Foranimalsinthisconditionhavepureblood，butverylittleofit，andthefatterananimalgetsthelessbecomesitssupplyofblood；forwhatsoeverisfatisdestituteofblood。
Afatsubstanceisincorruptible，butbloodandallthingscontainingitcorruptrapidly，andthispropertycharacterizesespeciallyallpartsconnectedwiththebones。Bloodisfinestandpurestinman；andthickestandblackestinthebullandtheass，ofallvivipara。Inthelowerandthehigherpartsofthebodybloodisthickerandblackerthaninthecentralparts。
Bloodbeatsorpalpitatesintheveinsofallanimalsalikeallovertheirbodies，andbloodistheonlyliquidthatpermeatestheentireframesoflivinganimals，withoutexceptionandatalltimes，aslongaslifelasts。Bloodisdevelopedfirstofallintheheartofanimalsbeforethebodyisdifferentiatedasawhole。Ifbloodberemovedorifitescapeinanyconsiderablequantity，animalsfallintoafaintorswoon；ifitberemovedorifitescapeinanexceedinglylargequantitytheydie。Ifthebloodgetexceedinglyliquid，animalsfallsick；forthebloodthenturnsintosomethinglikeichor，oraliquidsothinthatitattimeshasbeenknowntoexudethroughtheporeslikesweat。Insomecasesblood，whenissuingfromtheveins，doesnotcoagulateatall，oronlyhereandthere。Whilstanimalsaresleepingthebloodislessabundantlysuppliedneartheexteriorsurfaces，sothat，ifthesleepingcreaturebeprickedwithapin，theblooddoesnotissueascopiouslyasitwouldifthecreaturewereawake。Bloodisdevelopedoutofichorbycoction，andfatinlikemanneroutofblood。Ifthebloodgetdiseased，haemorrhoidsmayensueinthenostrilorattheanus，ortheveinsmaybecomevaricose。Blood，ifitcorruptinthebody，hasatendencytoturnintopus，andpusmayturnintoasolidconcretion。
Bloodinthefemalediffersfromthatinthemale，for，supposingthemaleandfemaletobeonaparasregardsageandgeneralhealth，thebloodinthefemaleisthickerandblackerthaninthemale；andwiththefemalethereisacomparativesuperabundanceofitintheinterior。Ofallfemaleanimalsthefemaleinmanisthemostrichlysuppliedwithblood，andofallfemaleanimalsthemenstruousdischargesarethemostcopiousinwoman。Thebloodofthesedischargesunderdiseaseturnsintoflux。Apartfromthemenstrualdischarges，thefemaleinthehumanspeciesislesssubjecttodiseasesofthebloodthanthemale。
Womenareseldomafflictedwithvaricoseveins，withhaemorrhoids，orwithbleedingatthenose，and，ifanyofthesemaladiessupervene，themensesareimperfectlydischarged。
Blooddiffersinquantityandappearanceaccordingtoage；inveryyounganimalsitresemblesichorandisabundant，intheolditisthickandblackandscarce，andinmiddle-agedanimalsitsqualitiesareintermediate。Inoldanimalsthebloodcoagulatesrapidly，evenbloodatthesurfaceofthebody；butthisisnotthecasewithyounganimals。Ichoris，infact，nothingelsebutunconcoctedblood:eitherbloodthathasnotyetbeenconcocted，orthathasbecomefluidagain。
20
Wenowproceedtodiscussthepropertiesofmarrow；forthisisoneoftheliquidsfoundincertainsanguineousanimals。Allthenaturalliquidsofthebodyarecontainedinvessels:asbloodinveins，marrowinbonesothermoisturesinmembranousstructuresoftheskinInyounganimalsthemarrowisexceedinglysanguineous，but，asanimalsgrowold，itbecomesfattyinanimalssuppliedwithfat，andsuet-likeinanimalswithsuet。Allbones，however，arenotsuppliedwithmarrow，butonlythehollowones，andnotallofthese。Forofthebonesinthelionsomecontainnomarrowatall，andsomeareonlyscantilysuppliedtherewith；andthataccounts，aswaspreviouslyobserved，forthestatementmadebycertainwritersthatthelionismarrowless。Inthebonesofpigsitisfoundinsmallquantities；
andinthebonesofcertainanimalsofthisspeciesitisnotfoundatall。
Theseliquids，then，arenearlyalwayscongenitalinanimals，butmilkandspermcomeatalatertime。Oftheselatter，thatwhich，whensoeveritispresent，issecretedinallcasesready-made，isthemilk；sperm，ontheotherhand，isnotsecretedoutinallcases，butinsomeonly，asinthecaseofwhataredesignatedthoriinfishes。
Whateveranimalshavemilk，haveitintheirbreasts。Allanimalshavebreaststhatareinternallyandexternallyviviparous，asforinstanceallanimalsthathavehair，asmanandthehorse；andthecetaceans，asthedolphin，theporpoise，andthewhale-fortheseanimalshavebreastsandaresuppliedwithmilk。Animalsthatareoviparousoronlyexternallyviviparoushaveneitherbreastsnormilk，asthefishandthebird。
Allmilkiscomposedofawateryserumcalled\'whey\'，andaconsistentsubstancecalledcurdorcheese；andthethickerthemilk，themoreabundantthecurd。Themilk，then，ofnon-ambidentalscoagulates，andthatiswhycheeseismadeofthemilkofsuchanimalsunderdomestication；butthemilkofambidentalsdoesnotcoagulate，northeirfateither，andthemilkisthinandsweet。Nowthecamel\'smilkisthethinnest，andthatofthehumanspeciesnextafterit，andthatoftheassnextagain，butcow\'smilkisthethickest。
Milkdoesnotcoagulateundertheinfluenceofcold，butratherrunstowhey；butundertheinfluenceofheatitcoagulatesandthickens。
Asageneralrulemilkonlycomestoanimalsinpregnancy。Whentheanimalispregnantmilkisfound，butforawhileitisunfitforuse，andthenafteranintervalofusefulnessitbecomesunfitforuseagain。Inthecaseoffemaleanimalsnotpregnantasmallquantityofmilkhasbeenprocuredbytheemploymentofspecialfood，andcaseshavebeenactuallyknownwherewomenadvancedinyearsonbeingsubmittedtotheprocessofmilkinghaveproducedmilk，andinsomecaseshaveproduceditinsufficientquantitiestoenablethemtosuckleaninfant。
ThepeoplethatliveonandaboutMountOetatakesuchshe-goatsasdeclinethemaleandrubtheiruddershardwithnettlestocauseanirritationamountingtopain；hereupontheymilktheanimals，procuringatfirstaliquidresemblingblood，thenaliquidmixedwithpurulentmatter，andeventuallymilk，asfreelyasfromfemalessubmittingtothemale。
Asageneralrule，milkisnotfoundinthemaleofmanorofanyotheranimal，thoughfromtimetotimeithasbeenfoundinamale；forinstance，onceinLemnosahe-goatwasmilkedbyitsdugsforithas，bytheway，twodugsclosetothepenis，andwasmilkedtosucheffectthatcheesewasmadeoftheproduce，andthesamephenomenonwasrepeatedinamaleofitsownbegetting。Suchoccurrences，however，areregardedassupernaturalandfraughtwithomenastofuturity，andinpointoffactwhentheLemnianowneroftheanimalinquiredoftheoracle，thegodinformedhimthattheportentforeshadowedtheacquisitionofafortune。Withsomemen，afterpuberty，milkcanbeproducedbysqueezingthebreasts；caseshavebeenknownwhereontheirbeingsubjectedtoaprolongedmilkingprocessaconsiderablequantityofmilkhasbeeneduced。
Inmilkthereisafattyelement，whichinclottedmilkgetstoresembleoil。Goat\'smilkismixedwithsheep\'smilkinSicily，andwhereversheep\'smilkisabundant。Thebestmilkforclottingisnotonlythatwherethecheeseismostabundant，butthatalsowherethecheeseisdriest。
Nowsomeanimalsproducenotonlyenoughmilktoreartheiryoung，butasuperfluousamountforgeneraluse，forcheese-makingandforstorage。Thisisespeciallythecasewiththesheepandthegoat，andnextindegreewiththecow。Mare\'smilk，bytheway，andmilkoftheshe-assaremixedinwithPhrygiancheese。Andthereismorecheeseincow\'smilkthaningoat\'smilk；forgrazierstellusthatfromninegallonsofgoat\'smilktheycangetnineteencheesesatanobolapiece，andfromthesameamountofcow\'smilk，thirty。Otheranimalsgiveonlyenoughofmilktoreartheiryoungwithal，andnosuperfluousamountandnonefittedforcheese-making，asisthecasewithallanimalsthathavemorethantwobreastsordugs；forwithnoneofsuchanimalsismilkproducedinsuperabundanceorusedforthemanufactureofcheese。
Thejuiceofthefigandrennetareemployedtocurdlemilk。Thefig-juiceisfirstsqueezedoutintowool；thewoolisthenwashedandrinsed，andtherinsingputintoalittlemilk，andifthisbemixedwithothermilkitcurdlesRennetisakindofmilk，foritisfoundinthestomachoftheanimalwhileitisyetsuckling。
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Rennetthenconsistsofmilkwithanadmixtureoffire，whichcomesfromthenaturalheatoftheanimal，asthemilkisconcocted。
Allruminatinganimalsproducerennet，and，ofambidentals，thehare。Rennetimprovesinqualitythelongeritiskept；andcow\'srennet，afterbeingkeptagoodwhile，andalsohare\'srennet，isgoodfordiarrhoea，andthebestofallrennetisthatoftheyoungdeer。
Inmilk-producinganimalsthecomparativeamountoftheyieldvarieswiththesizeoftheanimalandthediversitiesofpasturage。
Forinstance，thereareinPhasissmallcattlethatinallcasesgiveacopioussupplyofmilk，andthelargecowsinEpirusyieldeachonedailysomeninegallonsofmilk，andhalfofthisfromeachpairofteats，andthemilkerhastostanderect，stoopingforwardalittle，asotherwise，ifhewereseated，hewouldbeunabletoreachuptotheteats。But，withtheexceptionoftheass，allthequadrupedsinEpirusareoflargesize，andrelatively，thecattleandthedogsarethelargest。Nowlargeanimalsrequireabundantpasture，andthiscountrysuppliesjustsuchpasturage，andalsosuppliesdiversepasturegroundstosuitthediverseseasonsoftheyear。Thecattleareparticularlylarge，andlikewisethesheepoftheso-calledPyrrhicbreed，thenamebeinggiveninhonourofKingPyrrhus。
Somepasturequenchesmilk，asMediangrassorlucerne，andthatespeciallyinruminants；otherfeedingrendersitcopious，ascytisusandvetch；only，bytheway，cytisusinflowerisnotrecommended，asithasburningproperties，andvetchisnotgoodforpregnantkine，asitcausesincreaseddifficultyinparturition。
However，beaststhathaveaccesstogoodfeeding，astheyarebenefitedtherebyinregardtopregnancy，soalsobeingwellnourishedproducemilkinplenty。Someoftheleguminousplantsbringmilkinabundance，asforinstance，alargefeedofbeanswiththeewe，thecommonshe-goat，thecow，andthesmallshe-goat；forthisfeedingmakesthemdroptheirudders。And，bytheway，thepointingoftheuddertothegroundbeforeparturitionisasignoftherebeingplentyofmilkcoming。
Milkremainsforalongtimeinthefemale，ifshebekeptfromthemaleandbeproperlyfed，and，ofquadrupeds，thisisespeciallytrueoftheewe；fortheewecanbemilkedforeightmonths。Asageneralrule，ruminatinganimalsgivemilkinabundance，andmilkfittedforcheesemanufacture。IntheneighbourhoodofToronecowsrundryforafewdaysbeforecalving，andhavemilkalltherestofthetime。Inwomen，milkofalividcolourisbetterthanwhitefornursingpurposes；andswarthywomengivehealthiermilkthanfairones。Milkthatisrichestincheeseisthemostnutritious，butmilkwithascantysupplyofcheeseisthemorewholesomeforchildren。
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Allsanguineousanimalsejectsperm。Astowhat，andhow，itcontributestogeneration，thesequestionswillbediscussedinanothertreatise。Takingthesizeofhisbodyintoaccount，manemitsmorespermthananyotheranimal。Inhairy-coatedanimalsthespermissticky，butinotheranimalsitisnotso。Itiswhiteinallcases，andHerodotusisunderamisapprehensionwhenhestatesthattheAethiopiansejectblacksperm。
Spermissuesfromthebodywhiteandconsistent，ifitbehealthy，andafterquittingthebodybecomesthinandblack。Infrostyweatheritdoesnotcoagulate，butgetsexceedinglythinandwaterybothincolourandconsistency；butitcoagulatesandthickensundertheinfluenceofheat。Ifitbelonginthewombbeforeissuingout，itcomesmorethanusuallythick；andsometimesitcomesoutdryandcompact。Spermcapableofimpregnatingoroffructificationsinksinwater；spermincapableOfproducingthatresultdissolvesaway。ButthereisnotruthinwhatCtesiashaswrittenaboutthespermoftheelephant。
BookIV
1
Wehavenowtreated，inregardtobloodedanimalsofthepartstheyhaveincommonandofthepartspeculiartothisgenusorthat，andofthepartsbothcompositeandsimple，whetherwithoutorwithin。
Wenowproceedtotreatofanimalsdevoidofblood。Theseanimalsaredividedintoseveralgenera。
Onegenusconsistsofso-called\'molluscs\'；andbytheterm\'mollusc\'wemeanananimalthat，beingdevoidofblood，hasitsflesh-likesubstanceoutside，andanyhardstructureitmayhappentohave，inside-inthisrespectresemblingthered-bloodedanimals，suchasthegenusofthecuttle-fish。
Anothergenusisthatofthemalacostraca。Theseareanimalsthathavetheirhardstructureoutside，andtheirsoftorfleshlikesubstanceinside，andthehardsubstancebelongingtothemhastobecrushedratherthanshattered；andtothisgenusbelongsthecrawfishandthecrab。
Athirdgenusisthatoftheostracodermsor\'testaceans\'。Theseareanimalsthathavetheirhardsubstanceoutsideandtheirflesh-likesubstancewithin，andtheirhardsubstancecanbeshatteredbutnotcrushed；andtothisgenusbelongthesnailandtheoyster。
Thefourthgenusisthatofinsects；andthisgenuscomprehendsnumerousanddissimilarspecies。Insectsarecreaturesthat，asthenameimplies，havenickseitheronthebellyorontheback，oronbothbellyandback，andhavenoonepartdistinctlyosseousandnoonepartdistinctlyfleshy，butarethroughoutasomethingintermediatebetweenboneandflesh；thatistosay，theirbodyishardallthrough，insideandoutside。Someinsectsarewingless，suchastheiulusandthecentipede；somearewinged，asthebee，thecockchafer，andthewasp；andthesamekindisinsomecasesbothwingedandwingless，astheantandtheglow-worm。
Inmolluscstheexternalpartsareasfollows:inthefirstplace，theso-calledfeet；secondly，andattachedtothese，thehead；
thirdly，themantle-sac，containingtheinternalparts，andincorrectlydesignatedbysomewritersthehead；and，fourthly，finsroundaboutthesac。Seediagram。Inallmolluscstheheadisfoundtobebetweenthefeetandthebelly。Allmolluscsarefurnishedwitheightfeet，andinallcasesthesefeetareseverallyfurnishedwithadoublerowofsuckers，withtheexceptionofonesinglespeciesofpoulpeoroctopus。Thesepia，thesmallcalamaryandthelargecalamaryhaveanexceptionalorganinapairoflongarmsortentacles，havingattheirextremitiesaportionrenderedroughbythepresenceoftworowsofsuckers；andwiththesearmsortentaclestheyapprehendtheirfoodanddrawitintotheirmouths，andinstormyweathertheyclingbythemtoarockandswayaboutintheroughwaterlikeshipslyingatanchor。Theyswimbytheaidofthefinsthattheyhaveaboutthesac。Inallcasestheirfeetarefurnishedwithsuckers。
Theoctopus，bytheway，useshisfeelerseitherasfeetorhands；
withthetwowhichstandoverhismouthhedrawsinfood，andthelastofhisfeelersheemploysintheactofcopulation；andthislastone，bytheway，isextremelysharp，isexceptionalasbeingofawhitishcolour，andatitsextremityisbifurcate；thatistosay，ithasanadditionalsomethingontherachis，andbyrachisismeantthesmoothsurfaceoredgeofthearmonthefarsidefromthesuckers。
Seediagram。
Infrontofthesacandoverthefeelerstheyhaveahollowtube，bymeansofwhichtheydischargeanysea-waterthattheymayhavetakenintothesacofthebodyintheactofreceivingfoodbythemouth。Theycanshiftthetubefromsidetoside，andbymeansofittheydischargetheblackliquidpeculiartotheanimal。
Stretchingoutitsfeet，itswimsobliquelyinthedirectionoftheso-calledhead，andbythismodeofswimmingitcanseeinfront，foritseyesareatthetop，andinthisattitudeithasitsmouthattherear。The\'head\'，whilethecreatureisalive，ishard，andlooksasthoughitwereinflated。Itapprehendsandretainsobjectsbymeansoftheunder-surfaceofitsarms，andthemembraneinbetweenitsfeetiskeptatfulltension；iftheanimalgetontothesanditcannolongerretainitshold。
Thereisadifferencebetweentheoctopusandtheothermolluscsabovementioned:thebodyoftheoctopusissmall，andhisfeetarelong，whereasintheothersthebodyislargeandthefeetshort；soshort，infact，thattheycannotwalkonthem。Comparedwithoneanother，theteuthis，orcalamary，islong-shaped，andthesepiaflat-shaped；andofthecalamariestheso-calledteuthusismuchbiggerthantheteuthis；forteuthihavebeenfoundasmuchasfiveellslong。Somesepiaeattainalengthoftwoells，andthefeelersoftheoctopusaresometimesaslong，orevenlonger。Thespeciesteuthusisnotanumerousone；theteuthusdiffersfromtheteuthisinshape；thatis，thesharpextremityoftheteuthusisbroaderthanthatoftheother，and，further，theencirclingfingoesallroundthetrunk，whereasitisinpartlackingintheteuthis；bothanimalsarepelagic。
Inallcasestheheadcomesafterthefeet，inthemiddleofthefeetthatarecalledarmsorfeelers。Thereisheresituatedamouth，andtwoteethinthemouth；andabovethesetwolargeeyes，andbetwixttheeyesasmallcartilageenclosingasmallbrain；andwithinthemouthithasaminuteorganofafleshynature，andthisitusesasatongue，fornoothertonguedoesitpossess。Nextafterthis，ontheoutside，iswhatlookslikeasac；thefleshofwhichitismadeisdivisible，notinlongstraightstrips，butinannularflakes；
andallmolluscshaveacuticlearoundthisflesh。Nextafteroratthebackofthemouthcomesalongandnarrowoesophagus，andcloseafterthatacroporcraw，largeandspherical，likethatofabird；
thencomesthestomach，likethefourthstomachinruminants；andtheshapeofitresemblesthespiralconvolutioninthetrumpet-shell；
fromthestomachtheregoesbackagain，inthedirectionofthemouth，thingut，andthegutisthickerthantheoesophagus。Seediagram。
Molluscshavenoviscera，buttheyhavewhatiscalledamytis，andonitavesselcontainingathickblackjuice；inthesepiaorcuttle-fishthisvesselisthelargest，andthisjuiceismostabundant。Allmolluscs，whenfrightened，dischargesuchajuice，butthedischargeismostcopiousinthecuttle-fish。Themytis，then，issituatedunderthemouth，andtheoesophagusrunsthroughit；anddownbelowatthepointtowhichthegutextendsisthevesicleoftheblackjuice，andtheanimalhasthevesicleandthegutenvelopedinoneandthesamemembrane，andbythesamemembrane，sameorificedischargesboththeblackjuiceandtheresiduum。Theanimalshavealsocertainhair-likeorfurrygrowthsintheirbodies。
Inthesepia，theteuthis，andtheteuthusthehardpartsarewithin，towardsthebackofthebody；thosepartsarecalledinonethesepium，andintheotherthe\'sword\'。Theydifferfromoneanother，forthesepiuminthecuttle-fishandteuthusishardandflat，beingasubstanceintermediatebetweenboneandfishbone，withinpartacrumbling，spongytexture，butintheteuthisthepartisthinandsomewhatgristly。Thesepartsdifferfromoneanotherinshape，asdoalsothebodiesoftheanimals。Theoctopushasnothinghardofthiskindinitsinterior，butithasagristlysubstanceroundthehead，which，iftheanimalgrowsold，becomeshard。
Thefemalesdifferfromthemales。Themaleshaveaductinundertheoesophagus，extendingfromthemantle-cavitytothelowerportionofthesac，andthereisanorgantowhichitattaches，resemblingabreast；seediagraminthefemaletherearetwooftheseorgans，situatedhigherup；seediagramwithbothsexesthereareunderneaththeseorganscertainredformations。Theeggoftheoctopusissingle，unevenonitssurface，andoflargesize；thefluidsubstancewithinisalluniformincolour，smooth，andincolourwhite；thesizeoftheeggissogreatastofillavessellargerthanthecreature\'shead。Thesepiahastwosacs，andinsidethemanumberofeggs，likeinappearancetowhitehailstones。ForthedispositionofthesepartsImustrefertomyanatomicaldiagrams。
Themalesofalltheseanimalsdifferfromthefemales，andthedifferencebetweenthesexesismostmarkedinthesepia；forthebackofthetrunk，whichisblackerthanthebelly，isrougherinthemalethaninthefemale，andinthemalethebackisstriped，andtherumpismoresharplypointed。
Thereareseveralspeciesoftheoctopus。Onekeepsclosetothesurface，andisthelargestofthemall，andneartheshorethesizeislargerthanindeepwater；andthereareothers，small，variegatedincolour，whicharenotarticlesoffood。Therearetwoothers，onecalledtheheledone，whichdiffersfromitscongenersinthelengthofitslegsandinhavingonerowofsuckers-alltherestofthemolluscshavingtwo，-theothernicknamedvariouslythebolitainaorthe\'onion，\'andtheozolisorthe\'stinkard\'。
Therearetwoothersfoundinshellsresemblingthoseofthetestaceans。Oneofthemisnicknamedbysomepersonsthenautilusorthepontilus，orbyothersthe\'polypus\'egg\'；andtheshellofthiscreatureissomethinglikeaseparatevalveofadeepscallop-shell。
Thispolypuslivesveryoftenneartotheshore，andisapttobethrownuphighanddryonthebeach；underthesecircumstancesitisfoundwithitsshelldetached，anddiesbyandbyondryland。Thesepolypodsaresmall，andareshaped，asregardstheformoftheirbodies，likethebolbidia。Thereisanotherpolypusthatisplacedwithinashelllikeasnail；itnevercomesoutoftheshell，butlivesinsidetheshelllikethesnail，andfromtimetotimeprotrudesitsfeelers。
Somuchformolluscs。
2
WithregardtotheMalacostracaorcrustaceans，onespeciesisthatofthecrawfish，andasecond，resemblingthefirst，isthatofthelobster；thelobsterdifferingfromthecrawfishinhavingclaws，andinafewotherrespectsaswell。Anotherspeciesisthatofthecarid，andanotheristhatofthecrab，andtherearemanykindsbothofcaridandofcrab。
Ofcaridstherearetheso-calledcyphae，or\'hunch-backs\'，thecrangons，orsquillae，andthelittlekind，orshrimps，andthelittlekinddonotdevelopintoalargerkind。
Ofthecrab，thevarietiesareindefiniteandincalculable。ThelargestofallcrabsisonenicknamedMaia，asecondvarietyisthepagarusandthecrabofHeracleotis，andathirdvarietyisthefresh-watercrab；theothervarietiesaresmallerinsizeanddestituteofspecialdesignations。IntheneighbourhoodofPhoenicetherearefoundonthebeachcertaincrabsthatarenicknamedthe\'horsemen\'，fromtheirrunningwithsuchspeedthatitisdifficulttoovertakethem；thesecrabs，whenopened，areusuallyfoundempty，andthisemptinessmaybeputdowntoinsufficiencyofnutriment。
Thereisanothervariety，smalllikethecrab，butresemblinginshapethelobster。Alltheseanimals，ashasbeenstated，havetheirhardandshellypartoutside，wheretheskinisinotheranimals，andthefleshypartinside；andthebellyismoreorlessprovidedwithlamellae，orlittleflaps，andthefemaleheredepositsherspawn。
Thecrawfisheshavefivefeetoneitherside，includingtheclawsattheend；andinlikemannerthecrabshavetenfeetinall，includingtheclaws。Ofthecarids，thehunch-backed，orprawns，havefivefeetoneitherside，whicharesharp-pointed-thosetowardsthehead；andfiveothersoneithersideintheregionofthebelly，withtheirextremitiesflat；theyaredevoidofflapsontheundersidesuchasthecrawfishhas，butonthebacktheyresemblethecrawfish。Seediagram。Itisverydifferentwiththecrangon，orsquilla；ithasfourfrontlegsoneitherside，thenthreethinonesclosebehindoneitherside，andtherestofthebodyisforthemostpartdevoidoffeet。Seediagram。Ofalltheseanimalsthefeetbendoutobliquely，asisthecasewithinsects；andtheclaws，whereclawsarefound，turninwards。Thecrawfishhasatail，andfivefinsonit；andtheround-backedcaridhasatailandfourfins；thesquillaalsohasfinsatthetailoneitherside。Inthecaseofboththehump-backedcaridandthesquillathemiddleartofthetailisspinous:onlythatinthesquillathepartisflattenedandinthecariditissharp-pointed。Ofallanimalsofthisgenusthecrabistheonlyonedevoidofarump；and，whilethebodyofthecaridandthecrawfishiselongated，thatofthecrabisrotund。
Inthecrawfishthemalediffersfromthefemale:inthefemalethefirstfootisbifurcate，inthemaleitisundivided；thebelly-finsinthefemalearelargeandoverlappingontheneck，whileinthemaletheyaresmalleranddonotoverlap；and，further，onthelastfeetofthemaletherearespur-likeprojections，largeandsharp，whichprojectionsinthefemalearesmallandsmooth。
Bothmaleandfemalehavetwoantennaeinfrontoftheeyes，largeandrough，andotherantennaeunderneath，smallandsmooth。Theeyesofallthesecreaturesarehardandbeady，andcanmoveeithertotheinnerortotheouterside。Theeyesofmostcrabshaveasimilarfacilityofmovement，orrather，inthecrabthisfacilityisdevelopedinahigherdegree。Seediagram。
Thelobsterisallovergrey-coloured，withamottlingofblack。
Itsunderorhinderfeet，uptothebigfeetorclaws，areeightinnumber；thencomethebigfeet，farlargerandflatteratthetipsthanthesameorgansinthecrawfish；andthesebigfeetorclawsareexceptionalintheirstructure，fortherightclawhastheextremeflatsurfacelongandthin，whiletheleftclawhasthecorrespondingsurfacethickandround。Eachofthetwoclaws，dividedattheendlikeapairofjaws，hasbothbelowandaboveasetofteeth:onlythatintherightclawtheyareallsmallandsaw-shaped，whileintheleftclawthoseattheapexaresaw-shapedandthosewithinaremolar-shaped，theselatterbeing，intheunderpartofthecleftclaw，fourteethclosetogether，andintheupperpartthreeteeth，notclosetogether。Bothrightandleftclawshavetheupperpartmobile，andbringittobearagainstthelowerone，andbotharecurvedlikebandy-legs，beingtherebyadaptedforapprehensionandconstriction。Abovethetwolargeclawscometwoothers，coveredwithhair，alittleunderneaththemouth；andunderneaththesethegill-likeformationsintheregionofthemouth，hairyandnumerous。Theseorganstheanimalkeepsinperpetualmotion；andthetwohairyfeetitbendsanddrawsintowardsitsmouth。Thefeetnearthemoutharefurnishedalsowithdelicateoutgrowingappendages。Likethecrawfish，thelobsterhastwoteeth，ormandibles，andabovetheseteethareitsantennae，long，butshorterandfinerbyfarthanthoseofthecrawfish，andthenfourotherantennaesimilarinshape，butshorterandfinerthantheothers。Overtheseantennaecometheeyes，smallandshort，notlargeliketheeyesofthecrawfish。Overtheeyesisapeakyroughprojectionlikeaforehead，largerthanthesamepartinthecrawfish；
infact，thefrontalpartismorepointedandthethoraxismuchbroaderinthelobsterthaninthecrawfish，andthebodyingeneralissmootherandmorefullofflesh。Oftheeightfeet，fourarebifurcateattheextremities，andfourareundivided。Theregionoftheso-calledneckisoutwardlydividedintofivedivisions，andsixthlycomestheflattenedportionattheend，andthisportionhasfiveflaps，ortail-fins；andtheinnerorunderparts，intowhichthefemaledropsherspawn，arefourinnumberandhairy，andoneachoftheaforesaidpartsisaspineturnedoutwards，shortandstraight。
Thebodyingeneralandtheregionofthethoraxinparticulararesmooth，notroughasinthecrawfish；butonthelargeclawstheouterportionhaslargerspines。Thereisnoapparentdifferencebetweenthemaleandfemale，fortheybothhaveoneclaw，whicheveritmaybe，largerthantheother，andneithermalenorfemaleiseverfoundwithbothclawsofthesamesize。
Allcrustaceanstakeinwaterclosebythemouth。Thecrabdischargesit，closingup，asitdoesso，asmallportionofthesame，andthecrawfishdischargesitbywayofthegills；and，bytheway，thegill-shapedorgansinthecrawfishareverynumerous。
Thefollowingpropertiesarecommontoallcrustaceans:theyhaveinallcasestwoteeth，ormandiblesforthefrontteethinthecrawfisharetwoinnumber，andinallcasesthereisinthemouthasmallfleshystructureservingforatongue；andthestomachisclosetothemouth，onlythatthecrawfishhasalittleoesophagusinfrontofthestomach，andthereisastraightgutattachedtoit。Thisgut，inthecrawfishanditscongeners，andinthecarids，extendsinastraightlinetothetail，andterminateswheretheanimaldischargestheresiduum，andwherethefemaledepositsherspawn；inthecrabitterminateswheretheflapissituated，andinthecentreoftheflap。Andbytheway，inalltheseanimalsthespawnisdepositedoutside。Further，thefemalehastheplaceforthespawnrunningalongthegut。And，again，alltheseanimalshave，moreorless，anorgantermedthe\'mytis\'，or\'poppyjuice\'。
Wemustnowproceedtoreviewtheirseveraldifferentiae。
Thecrawfishthen，ashasbeensaid，hastwoteeth，largeandhollow，inwhichiscontainedajuiceresemblingthemytis，andinbetweentheteethisafleshysubstance，shapedlikeatongue。Afterthemouthcomesashortoesophagus，andthenamembranousstomachattachedtotheoesophagus，andattheorificeOfthestomacharethreeteeth，twofacingoneanotherandathirdstandingbyitselfunderneath。Comingoffatabendfromthestomachisagut，simpleandofequalthicknessthroughouttheentirelengthofthebodyuntilitreachestheanalvent。