THE PRIMARY TYPES OP FORM. 105 



whales (forming the natatorial order of the Mam- 

 malia) ; the swimming order of birds ; and the Sauri, or 

 aquatic reptiles ! As to the economy of aquatic types^ 

 we have already premised that they are almost entirely 

 carnivorous. In those that belong to quadrupeds and 

 birdsj the food is seized by the mouth alone ; the feet 

 being slightly, and often not at all, developed : and all 

 such as do not wander in search of their prey, dart 

 upon it from a fixed station." This is the substance 

 of what was formerly advanced regarding the aquatic 

 types of all animals, and we are now to determine 

 whether the cartilaginous order of fishes does not accord 

 with this theoretical description. Independent of the 

 nature of their bones^ they can be immediately recog- 

 nised from aU other fish by the muzzle being so 

 enlarged and produced beyond the jaws as to alter the 

 position of the mouthy which is actually placed beneath 

 the head — not, as in all other fishes, at its termination. 

 The sharks, no less than the rays, are the most gigantic 

 monsters among fish ; and that they are eminently car- 

 nivorous is unfortunately too true, since the first are 

 declared enemies to the human race. The great size 

 of the head observed in the aquatic Mammalia is not 

 equally conspicuous in the same type among fish, 

 although none have their head larger in proportion to 

 their body than these; and such is the pecuhar shape 

 of the ray, that they seem, like their prototypes the 

 Crustacea, to have the head confounded with the 

 thorax and body, so as to give the impression that all 

 three parts were united in order to form an enormous 

 head. The fishes of this family, which we place at the 

 head of the Cartilagines, seem also to possess the habit 

 of natatorial birds, in lying in wait for their prey, 

 and darting upon it from a fixed station ; while their 

 viviparous nature is at once explained, when we re- 

 collect that these creatures effect the passage between 

 fishes and aquatic Mammalia. There can be no doubt, 

 in short, that in the Cartilaoines we have an exem- 

 plification of the natatorial type. 



