a history of science-4-第18部分

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independent　of　the　power　of　the　heartviz。；　that　beginning　at　the　termination　of　the　veins　of　the　gills　and　branching　through　the　muscles；　and　that　which　passes　through　the　liver；　both　which　are　carried　on　by　the　action　of　those　respective　arteries　and　veins。〃＇6＇

Darwin　is　here　a　trifle　fanciful　in　forcing　the　analogy　between　plants　and　animals。　　The　circulatory　system　of　plants　is　really　not　quite　so　elaborately　comparable　to　that　of　fishes　as　he　supposed。　But　the　all…important　idea　of　the　uniformity　underlying　the　seeming　diversity　of　Nature　is　here　exemplified；　as　elsewhere　in　the　writings　of　Erasmus　Darwin；　and；　more　specifically；　a　clear　grasp　of　the　essentials　of　the　function　of　respiration　is　fully　demonstrated。


ZOOLOGY　AT　THE　CLOSE　OF　THE　EIGHTEENTH　CENTURY


Several　causes　conspired　to　make　exploration　all　the　fashion　during　the　closing　epoch　of　the　eighteenth　century。　New　aid　to　the　navigator　had　been　furnished　by　the　perfected　compass　and　quadrant；　and　by　the　invention　of　the　chronometer；　medical　science　had　banished　scurvy；　which　hitherto　had　been　a　perpetual　menace　to　the　voyager；　and；　above　all；　the　restless　spirit　of　the　age　impelled　the　venturesome　to　seek　novelty　in　fields　altogether　new。　　Some　started　for　the　pole；　others　tried　for　a　northeast　or　northwest　passage　to　India；　yet　others　sought　the　great　fictitious　antarctic　continent　told　of　by　tradition。　All　these　of　course　failed　of　their　immediate　purpose；　but　they　added　much　to　the　world's　store　of　knowledge　and　its　fund　of　travellers'　tales。

Among　all　these　tales　none　was　more　remarkable　than　those　which　told　of　strange　living　creatures　found　in　antipodal　lands。　And　here；　as　did　not　happen　in　every　field；　the　narratives　were　often　substantiated　by　the　exhibition　of　specimens　that　admitted　no　question。　Many　a　company　of　explorers　returned　more　or　less　laden　with　such　trophies　from　the　animal　and　vegetable　kingdoms；　to　the　mingled　astonishment；　delight；　and　bewilderment　of　the　closet　naturalists。　The　followers　of　Linnaeus　in　the　〃golden　age　of　natural　history；〃　a　few　decades　before；　had　increased　the　number　of　known　species　of　fishes　to　about　four　hundred；　of　birds　to　one　thousand；　of　insects　to　three　thousand；　and　of　plants　to　ten　thousand。　But　now　these　sudden　accessions　from　new　territories　doubled　the　figure　for　plants；　tripled　it　for　fish　and　birds；　and　brought　the　number　of　described　insects　above　twenty　thousand。　　Naturally　enough；　this　wealth　of　new　material　was　sorely　puzzling　to　the　classifiers。　The　more　discerning　began　to　see　that　the　artificial　system　of　Linnaeus；　wonderful　and　useful　as　it　had　been；　must　be　advanced　upon　before　the　new　material　could　be　satisfactorily　disposed　of。　The　way　to　a　more　natural　system；　based　on　less　arbitrary　signs；　had　been　pointed　out　by　Jussieu　in　botany；　but　the　zoologists　were　not　prepared　to　make　headway　towards　such　a　system　until　they　should　gain　a　wider　understanding　of　the　organisms　with　which　they　had　to　deal　through　comprehensive　studies　of　anatomy。　Such　studies　of　individual　forms　in　their　relations　to　the　entire　scale　of　organic　beings　were　pursued　in　these　last　decades　of　the　century；　but　though　two　or　three　most　important　generalizations　were　achieved　（notably　Kaspar　Wolff's　conception　of　the　cell　as　the　basis　of　organic　life；　and　Goethe's　all…important　doctrine　of　metamorphosis　of　parts）；　yet；　as　a　whole；　the　work　of　the　anatomists　of　the　period　was　germinative　rather　than　fruit…bearing。　Bichat's　volumes；　telling　of　the　recognition　of　the　fundamental　tissues　of　the　body；　did　not　begin　to　appear　till　the　last　year　of　the　century。　The　announcement　by　Cuvier　of　the　doctrine　of　correlation　of　parts　bears　the　same　date；　but　in　general　the　studies　of　this　great　naturalist；　which　in　due　time　were　to　stamp　him　as　the　successor　of　Linnaeus；　were　as　yet　only　fairly　begun。



　V。　ANATOMY　AND　PHYSIOLOGY　IN　THE　NINETEENTH　CENTURY

CUVIER　AND　THE　CORRELATION　OF　PARTS

We　have　seen　that　the　focal　points　of　the　physiological　world　towards　the　close　of　the　eighteenth　century　were　Italy　and　England；　but　when　Spallanzani　and　Hunter　passed　away　the　scene　shifted　to　France。　　The　time　was　peculiarly　propitious；　as　the　recent　advances　in　many　lines　of　science　had　brought　fresh　data　for　the　student　of　animal　life　which　were　in　need　of　classification；　and；　as　several　minds　capable　of　such　a　task　were　in　the　field；　it　was　natural　that　great　generalizations　should　have　come　to　be　quite　the　fashion。　Thus　it　was　that　Cuvier　came　forward　with　a　brand…new　classification　of　the　animal　kingdom；　establishing　four　great　types　of　being；　which　he　called　vertebrates；　mollusks；　articulates；　and　radiates。　Lamarck　had　shortly　before　established　the　broad　distinction　between　animals　with　and　those　without　a　backbone；　Cuvier's　Classification　divided　the　latterthe　invertebratesinto　three　minor　groups。　And　this　division；　familiar　ever　since　to　all　students　of　zoology；　has　only　in　very　recent　years　been　supplanted；　and　then　not　by　revolution；　but　by　a　further　division；　which　the　elaborate　recent　studies　of　lower　forms　of　life　seemed　to　make　desirable。

In　the　course　of　those　studies　of　comparative　anatomy　which　led　to　his　new　classification；　Cuvier's　attention　was　called　constantly　to　the　peculiar　co…ordination　of　parts　in　each　individual　organism。　Thus　an　animal　with　sharp　talons　for　catching　living　preyas　a　member　of　the　cat　tribehas　also　sharp　teeth；　adapted　for　tearing　up　the　flesh　of　its　victim；　and　a　particular　type　of　stomach；　quite　different　from　that　of　herbivorous　creatures。　This　adaptation　of　all　the　parts　of　the　animal　to　one　another　extends　to　the　most　diverse　parts　of　the　organism；　and　enables　the　skilled　anatomist；　from　the　observation　of　a　single　typical　part；　to　draw　inferences　as　to　the　structure　of　the　entire　animala　fact　which　was　of　vast　aid　to　Cuvier　in　his　studies　of　paleontology。　It　did　not　enable　Cuvier；　nor　does　it　enable　any　one　else；　to　reconstruct　fully　the　extinct　animal　from　observation　of　a　single　bone；　as　has　sometimes　been　asserted；　but　what　it　really　does　establish；　in　the　hands　of　an　expert；　is　sufficiently　astonishing。

〃While　the　study　of　the　fossil　remains　of　the　greater　quadrupeds　is　more　satisfactory；〃　he　writes；　〃by　the　clear　results　which　it　affords；　than　that　of　the　remains　of　other　animals　found　in　a　fossil　state；　it　is　also　complicated　with　greater　and　more　numerous　difficulties。　Fossil　shells　are　usually　found　quite　entire；　and　retaining　all　the　characters　requisite　for　comparing　them　with　the　specimens　contained　in　collections　of　natural　history；　or　represented　in　the　works　of　naturalists。　Even　the　skeletons　of　fishes　are　found　more　or　less　entire；　so　that　the　general　forms　of　their　bodies　can；　for　the　most　part；　be　ascertained；　and　usually；　at　least；　their　generic　and　specific　characters　are　determinable；　as　these　are　mostly　drawn　from　their　solid　parts。　In　quadrupeds；　on　the　contrary；　even　when　their　entire　skeletons　are　found；　there　is　great　difficulty　in　discovering　their　distinguishing　characters；　as　these　are　chiefly　founded　upon　their　hairs　and　colors　and　other　marks　which　have　disappeared　previous　to　their　incrustation。　It　is　also　very　rare　to　find　any　fossil　skeletons　of　quadrupeds　in　any　degree　approaching　to　a　complete　state；　as　the　strata　for　the　most　part　only　contain　separate　bones；　scattered　confusedly　and　almost　always　broken　and　reduced　to　fragments；　which　are　the　only　means　left　to　naturalists　for　ascertaining　the　species　or　genera　to　which　they　have　belonged。

〃Fortunately　comparative　anatomy；　when　thoroughly　understood；　enables　us　to　surmount　all　these　difficulties；　as　a　careful　application　of　its　principles　instructs　us　in　the　correspondences　and　dissimilarities　of　the　forms　of　organized　bodies　of　different　kinds；　by　which　each　may　be　rigorously　ascertained　from　almost　every　fragment　of　its　various　parts　and　organs。

〃Every　organized　individual　forms　an　entire　system　of　its　own；　all　the　parts　of　which　naturally　correspond；　and　concur　to　produce　a　certain　definite　purpose；　by　reciprocal　reaction；　or　by　combining　towards　the　same　end。　　Hence　none　of　these　separate　parts　can　change　their　forms　without　a　corresponding　change　in　the　other　parts　of　the　same　animal；　and　consequently　each　of　these　parts；　taken　separately；　indicates　all　the　other　parts　to　which　it　has　belonged。　　Thus；　as　I　have　elsewhere　shown；　if　the　viscera　of　an　animal　are　so　organized　as　only　to　be　fitted　for　the　digestion　of　recent　flesh；　it　is　also　requisite　that　the　jaws　should　be　so　constructed　as　to　fit　them　for　devouring　prey；　the　claws　must　be　constructed　for　seizing　and　tearing　it　to　pieces；　the　teeth　for　cutting　and　dividing　its　flesh；　the　entire　system　of　the　limbs；　or　organs　of　motion；　for　pursuing　and　overtaking　it；　and　the　organs　of　sense　for　discovering　it　at　a　distance。　Nature　must　also　have　endowed　the　brain　of　the　animal　with　instincts　sufficient　for　concealing　itself　and　for　laying　plans　to　catch　its　necessary　victims。　　。　。　。　。　。　。　。　。　。

〃To　enable　the　animal　to　carry　off　its　prey　when　seized；　a　corresponding　force　is　requisite　in　the　muscles　which　elevate　the　head；　and　this　necessarily　gives　rise　to　a　determinate　form　of　the　vertebrae　to　which　these　muscles　are　attached　and　of