on the gait of animals-第6章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！




divide　the　air　or　water　most　quickly　and　with　most　force　and　so　effect



their　movement。　For　the　hinder　parts　in　this　way　would　follow　forwards



as　they　are　carried　along　in　the　yielding　medium；　fish　in　the　water；



birds　in　the　air。



　　Of　oviparous　quadrupeds　all　those　that　live　in　holes；　like



crocodiles；　lizards；　spotted　lizards；　freshwater　tortoises；　and



turtles；　have　their　legs　attached　obliquely　as　their　whole　body



sprawls　over　the　ground；　and　bend　them　obliquely。　The　reason　is　that



this　is　useful　for　ease　in　creeping　into　holes；　and　for　sitting　upon



their　eggs　and　guarding　them。　And　as　they　are　splayed　outwards　they



must　of　necessity　tuck　in　their　thighs　and　put　them　under　them　in



order　to　achieve　the　lifting　of　the　whole　body。　In　view　of　this　they



cannot　bend　them　otherwise　than　outwards。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　16







　　We　have　already　stated　the　fact　that　non…sanguineous　animals　with



limbs　are　polypods　and　none　of　them　quadrupeds。　And　the　reason　why



their　legs；　except　the　extreme　pairs；　were　necessarily　attached



obliquely　and　had　their　flexions　upwards；　and　the　legs　themselves　were



somewhat　turned　under　（bandy…shape）　and　backwards　is　plain。　In　all



such　creatures　the　intermediate　legs　both　lead　and　follow。　If　then



they　lay　under　them；　they　must　have　had　their　flexion　both　forwards



and　backwards；　on　account　of　leading；　forwards；　and　on　account　of



following；　backwards。　Now　since　they　have　to　do　both；　for　this



reason　their　limbs　are　turned　under　and　bent　obliquely；　except　the　two



extreme　pairs。　（These　two　are　more　natural　in　their　movement；　the



front　leading　and　the　back　following。）　Another　reason　for　this　kind　of



flexion　is　the　number　of　their　legs；　arranged　in　this　way　they　would



interfere　less　with　one　another　in　progression　and　not　knock　together。



But　the　reason　that　they　are　bandy　is　that　all　of　them　or　most　of　them



live　in　holes；　for　creatures　living　so　cannot　possibly　be　high　above



the　ground。



　　But　crabs　are　in　nature　the　oddest　of　all　polypods；　they　do　not



progress　forwards　except　in　the　sense　explained　above；　they　are　the



only　animals　which　have　more　than　one　pair　of　leading　limbs。　The



explanation　of　this　is　the　hardness　of　their　limbs；　and　the　fact



that　they　use　them　not　for　swimming　but　for　walking；　they　always



keep　on　the　ground。　However；　the　flexion　of　the　limbs　of　all



polypods　is　oblique；　like　that　of　the　quadrupeds　which　live　in



holes…for　example　lizards　and　crocodiles　and　most　of　the　oviparous



quadrupeds。　And　the　explanation　is　that　some　of　them　in　their　breeding



periods；　and　some　all　their　life；　live　in　holes。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　17







　　Now　the　rest　have　bandy　legs　because　they　are　soft…skinned；　but



the　crayfish　is　hard…skinned　and　its　limbs　are　for　swimming　and　not



for　walking　（and　so　are　not　bandy）。　Crabs；　too；　have　their　limbs



bent　obliquely；　but　not　bandy　like　oviparous　quadrupeds　and



non…sanguineous　polypods；　because　their　limbs　have　a　hard　and



shell…like　skin；　although　they　don't　swim　but　live　in　holes；　they　live



in　fact　on　the　ground。　Moreover；　their　shape　is　like　a　disk；　as



compared　with　the　crayfish　which　is　elongated；　and　they　haven't　a　tail



like　the　crayfish；　a　tail　is　useful　to　the　crayfish　for　swimming；



but　the　crab　is　not　a　swimming　creature。　Further；　it　alone　has　its



side　equivalent　to　a　hinder　part；　because　it　has　many　leading　feet。



The　explanation　of　this　is　that　its　flexions　are　not　forward　nor　its



legs　turned　in　under　（bandy）。　We　have　given　above　the　reason　why　its



legs　are　not　turned　in　under；　that　is　the　hardness　and　shell…like



character　of　its　integument。



　　For　these　reasons　then　it　must　lead　off　with　more　than　one　limb；　and



move　obliquely；　obliquely；　because　the　flexion　is　oblique；　and　with



more　than　one　limb；　because　otherwise　the　limbs　that　were　still



would　have　got　in　the　way　of　those　that　were　moving。



　　Fishes　of　the　flat　kind　swim　with　their　heads　twisted；　as　one…eyed



men　walk；　they　have　their　natural　shape　distorted。　Web…footed　birds



swim　with　their　feet；　because　they　breath　the　air　and　have　lungs



they　are　bipeds；　but　because　they　have　their　home　in　the　water　they



are　webbed；　by　this　arrangement　their　feet　serve　them　instead　of　fins。



They　have　their　legs　too；　not　like　the　rest　of　birds　in　the　centre



of　their　body；　but　rather　set　back。　Their　legs　are　short；　and　being



set　back　are　serviceable　for　swimming。　The　reason　for　their　having



short　legs　is　that　nature　has　added　to　their　feet　by　subtracting



from　the　length　of　their　limbs；　instead　of　length　she　gives



stoutness　to　the　legs　and　breadth　to　the　feet。　Broad　feet　are　more



useful　than　long　for　pushing　away　the　water　when　they　are　swimming。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　18







　　There　is　reason；　too；　for　winged　creatures　having　feet；　but　fish



none。　The　former　have　their　home　in　the　dry　medium；　and　cannot



remain　always　in　mid　air；　they　must　therefore　have　feet。　Fish　on　the



contrary　live　in　the　wet　medium；　and　take　in　water；　not　air。　Fins



are　useful　for　swimming；　but　feet　not。　And　if　they　had　both　they　would



be　non…sanguineous。　There　is　a　broad　similarity　between　birds　and



fishes　in　the　organs　of　locomotion。　Birds　have　their　wings　on　the



superior　part；　similarly　fish　have　two　pectoral　fins；　again；　birds



have　legs　on　their　under　parts　and　near　the　wings；　similarly；　most



fish　have　two　fins　on　the　under　parts　and　near　the　pectorals。　Birds；



too；　have　a　tail　and　fish　a　tail…fin。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　19







　　A　difficulty　may　be　suggested　as　to　the　movements　of　molluscs；



that　is；　as　to　where　that　movement　originates；　for　they　have　no



distinction　of　left　and　right。　Now　observation　shows　them　moving。　We



must；　I　think；　treat　all　this　class　as　mutilated；　and　as　moving　in　the



way　in　which　limbed　creatures　do　when　one　cuts　off　their　legs；　or　as



analogous　with　the　seal　and　the　bat。　Both　the　latter　are　quadrupeds



but　misshapen。　Now　molluscs　do　move；　but　move　in　a　manner　contrary



to　nature。　They　are　not　moving　things；　but　are　moving　if　as



sedentary　creatures　they　are　compared　with　zoophytes；　and　sedentary　if



classed　with　progressing　animals。



　　As　to　right　and　left；　crabs；　too；　show　the　distinction　poorly；　still



they　do　show　it。　You　can　see　it　in　the　claw；　the　right　claw　is



larger　and　stronger；　as　though　the　right　and　left　sides　were　trying　to



get　distinguished。



　　The　structure　of　animals；　both　in　their　other　parts；　and



especially　in　those　which　concern　progression　and　any　movement　in



place；　is　as　we　have　now　described。　It　remains；　after　determining



these　questions；　to　investigate　the　problems　of　Life　and　Death。











　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　…THE　END…



。