Now，withtheincreasedsizeandchangeddirectionoftheearsnotonlyhasthebonyauditorymeatusbecomechangedinoutline，direction，andgreatlyinsize，butthewholeskullhasbeenslightlymodified。Thiscouldbeclearlyseenin\"half—lops\"——thatis，inrabbitswithonlyoneearloppingforward——
fortheoppositesidesoftheirskullswerenotstrictlysymmetrical。Thisseemstomeacuriousinstanceofcorrelation，betweenhardbonesandorganssosoftandflexible，aswellassounimportantunderaphysiologicalpointofview，astheexternalears。Theresultnodoubtislargelyduetomeremechanicalaction，thatis，totheweightoftheears，onthesameprinciplethattheskullofahumaninfantiseasilymodifiedbypressure。
Theskinandtheappendagesofhair，feathers，hoofs，horns，andteeth，arehomologousoverthewholebody。Everyoneknowsthatthecolouroftheskinandthatofthehairusuallyvarytogether;sothatVirgiladvisestheshepherdtolookwhetherthemouthandtongueoftheramareblack，lestthelambsshouldnotbepurelywhite。Thecolouroftheskinandhair，andtheodouremittedbytheglandsoftheskin，aresaid（25/10。Godron’Surl’Espece’tome2page217。）tobeconnected，eveninthesameraceofmen。
Generallythehairvariesinthesamewayalloverthebodyinlength，fineness，andcurliness。Thesameruleholdsgoodwithfeathers，asweseewiththelacedandfrizzledbreedsbothoffowlsandpigeons。Inthecommoncockthefeathersontheneckandloinsarealwaysofaparticularshape，calledhackles:nowinthePolishbreed，bothsexesarecharacterisedbyatuftoffeathersonthehead，andthroughcorrelationthesefeathersinthemalealwaysassumetheformofhackles。Thewingandtail—feathers，thougharisingfrompartsnothomologous，varyinlengthtogether;sothatlongorshortwingedpigeonsgenerallyhavelongorshorttails。ThecaseoftheJacobin—pigeonismorecurious，forthewingandtailfeathersareremarkablylong;andthisapparentlyhasarisenincorrelationwiththeelongatedandreversedfeathersonthebackoftheneck，whichformthehood。
Thehoofsandhairarehomologousappendages;andacarefulobserver，namelyAzara（25/11。’QuadrupedesduParaguay’tome2page333。），statesthatinParaguayhorsesofvariouscoloursareoftenbornwiththeirhaircurledandtwistedlikethatontheheadofanegro。Thispeculiarityisstronglyinherited。Butwhatisremarkableisthatthehoofsofthesehorses\"areabsolutelylikethoseofamule。\"Thehairalsooftheirmanesandtailsisinvariablymuchshorterthanusual，beingonlyfromfourtotwelveinchesinlength;sothatcurlinessandshortnessofthehairarehere，aswiththenegro，apparentlycorrelated。