IntheCalamariesandthePoulpstheink-bagisplacedintheupperpartofthebody，incloseproximitytothemytis，whereasintheSepiaitislowerdown，againstthestomach。FortheSepiahasamoreplentifulsupplyofinkthantherest，inasmuchasitmakesmoreuseofit。Thereasonsforthisare，firstly，thatitlivesneartheshore，and，secondly，thatithasnoothermeansofprotection；whereasthePoulphasitslongtwiningfeettouseinitsdefence，andis，moreover，endowedwiththepowerofchangingcolour。Thischangingofcolour，likethedischargeofink，occursastheresultoffright。AstotheCalamary，itlivesfaroutatsea，beingtheonlyoneoftheCephalopodathatdoesso；andthisgivesitprotection。ThesethenarethereasonswhytheinkismoreabundantintheSepiathanintheCalamary，andthisgreaterabundanceexplainsthelowerposition；foritallowstheinktobeejectedwitheaseevenfromadistance。Theinkitselfisofanearthycharacter，inthisresemblingthewhitedepositonthesurfaceofabird’sexcrementandtheexplanationinbothcasesisthesame，namely，theabsenceofaurinarybladder。For，indefaultofthis，itistheinkthatservesfortheexcretionoftheearthiestmatter。
AndthisismoreespeciallythecaseintheSepia，becausethereisagreaterproportionofearthinitscompositionthaninthatoftheotherCephalopoda。Theearthycharacterofitsboneisaclearindicationofthis。ForinthePoulpthereisnoboneatall，andintheCalamaryitisthinandcartilaginous。WhythisboneshouldbepresentinsomeCephalopoda，andwantinginothers，andhowitscharactervariesinthosethathaveit，hasnowbeensetforth。
Theseanimals，havingnoblood，areinconsequencecoldandofatimidcharacter。Now，insomeanimals，fearcausesadisturbanceofthebowels，and，inothers，aflowofurinefromthebladder。
Similarlyintheseitproducesadischargeofink，and，thoughtheejectionofthisinkinfright，likethatoftheurine，istheresultofnecessity，and，thoughitisofexcrementalcharacter，yetitisusedbynatureforapurpose，namely，theprotectionandsafetyoftheanimalthatexcretesit。
TheCrustaceaalso，boththeCaraboidformsandtheCrabs，areprovidedwithteeth，namelytheirtwoanteriorteeth；andbetweenthesetheyalsopresentthetongue-likepieceofflesh，ashasindeedbeenalreadymentioned。Directlyaftertheirmouthcomesagullet，which，ifwecomparerelativesizes，isbutsmallinproportiontothebody：andthenastomach，whichintheCarabiandsomeoftheCrabsisfurnishedwithasecondsetofteeth，theanteriorteethbeinginsufficientforadequatemastication。Fromthestomachauniformgutrunsinadirectlinetotheexcrementalvent。