SKELETON 



bolic of that sphere in Nature in which they 

 are destined to live and act. The two main 

 primary divisions of differential forms are symbolise 



Fig. 493. 



676 



those of aquatic and terrestrial animals. The 

 aquatic class, inhabiting the watery regions, 

 their native element, in which 



The caudal apparatus of the osseous fish (Pleuronectidce). 



they move submerged ; and accordingly we prone upon the earth, produce the locomotive 



find them treading this medium by loco- organs suited to that motion, viz. on the 



motive members arranged dorsad as well as ventral side only, 



ventrad ; while the terrestrial class, moving All species of the class of fishes approach 



Fig. 494. 



The uniform archetypal spinal series, 

 Showing how the species or variety is proportioned from it as the plus quantity. 



nearer to the plus uniform character of the motive or fin member dorsad, whereas no 

 serial axis (fig. 494.) than any of the species of species of the terrestrial-moving class requires 

 the terrestrial class ; for all species of the any form of such a member. Even the mam- 

 former class produce some form of the loco- malian cetaceans are furnished with a remnant 



xx 2 



