da VEKTEBRATE ANIMALS. 



respiration is moderate, arc gcncrany lormea to waiK and run with precision and 

 vigour ; the birds, in which it is greater, have tlic muscular energy and lightness 

 necessary for flight; tlie re]itiles, where it is diminished, are condemned to creep, and 

 many of them pass a portion of their life in a state of torpor ; the fishes, in fine, 

 to execute their movements, require to be supported in a fluid specifically almost as 

 heavy as themselves.* 



All the circumstances of organization proj)er to each of these four classes, and 

 especially those -which refer to motion and the external senses, have a necessfiry 

 relation with these essential characters. 



The class of mammalians, however, has pjeculiar characters in its viviparous mode of 

 generation, in the manner in which the foetus is nourished in the womb by means of 

 the placenta, and in the mamma; by which they suckle their young. 



The other classes are, on the contrary, oviparous ; and if we ])lace them together, in 

 opjjosition to the first, there will be jjerceived numerous resemblances which announce, 

 on their part, a special plan of organization, subordinate to the great general plan of 

 all the verteljrates. 



THE FIRST CLASS OF VERTEBRATE ANIMALS. 



MAMMALIA. 



Mammalians require to be placed at the head of the animal kingdom, not only 

 because thi.s is the class to "which we ourselves belong, but also because it is that which 

 enjo3\s the most numerous faculties, the most dehcate sensations, the most varied 

 powers of motion, and in which all the (hffercrit qualities seem together combined to 

 produce a more perfect degree ol intelligence, — the one most fertile in resources, most 

 susceptible of perfection, and least the shive of instinct. 



As their quantity of respiration is moderate, they are in general designed for walking 

 on the ground, but with vigorous and continued steps. Consequently, all the articula- 

 tions of their skuk'ton have very precise forms, which rigorously determine their motions. 



Some of them, however, by means ot lengthened limbs and extended membranes, 

 raise themselves in the air; others have the limbs so shortened, that thev can employ 

 them with effect only in water ; hut they do not the more on this account lose the 

 sreneral characters of the class. 



* To clcji.enil tn pnrticuhir tns<-s, liowcvcr, it ^vnulr.l nppcar tliat 

 species may be fniincil on riimost every type, even very subonliunle 

 types, fi)r any piirticular mtidc of life. Thus, to illustrnte bricHy, the 

 huts, wliieli are true niFuniuiiliaas, nrc modificil for iierittl progjes.siou 

 like birds ; find tlie whales, other nmmmnllan.s, liiive a fish-like exterior, 

 lyeifig lieslffned lo live exelusively in water : so there are birrfa wliieh 

 are utterly inenpable of fli(fht ; some, as tlie ostrich, adapted to seour 

 the plains, like a quiLdnipcd ; othera, as tlie peng-uin.s, whose only 

 sphere of activity is in the writer: the pterodactylc alTords an ex- 

 ample of a genus of flying reptiles, Ihc fossil remains of whicli only 

 have been discovered. Uescciidinjr to lower groups, we find among 

 tdrdfl, a g-cnus of thrushes (C-VV/c/uh), wliieb seeks its subsistence U7ider 

 wilier; and another of totipalinate water-fowl (T/ichyp/'li'.i), wluch 



BToup'; which ttiey approximate in hnbit,— luniu'-ht ihnt crxn be ret^firdeil 

 IIS nil iiitcnriiiii^il or designed rrprrsentdti'-n of Ihcm, aa li;is some- 

 times been iuwigined : for it is evident, that if species based on two 

 dilTcreiit plans of orifanization are respectively modified to perform 

 the same office in the economy of nature, they must nceessiirily re- 

 semble, to a certain extent, superficially, as a consequence of that 

 adaptation ; while there are many cases also in each class which can- 

 not well be represented in some others, as that of the mole among 

 quadrupeds, which has no counterpart or correspondent group In the 

 class of birds. Habit, or mode of life, has indeed nolirtng whatever 

 to do witli the physiolog-ical relations of organisms, which alTord the 

 only legitimate basis of classification ; and those special modifications 

 to particular habits, which, occurring alike In any class, superinduce 

 ms nor nivcs. .->uch dcvinlions. liovvovcr, fri)m the general ^ a resemhlaiicc in snpcrficial characler'; only, conslitiilc mIdii h;is been 

 t their allied genera, have no iutriiislcr.l relaUu,, to (he ' well di-,L)ni,.ui.shcd by the term >n,at<,gy, as opposed t„ ./jA/, /(y.— Ed. 



