LOCOMOTION OF FISHES. '245 



the individual economy ; but not, therefore, that it is an absolute 

 elevation of such parts in the series of animal tissues. 



It has been deemed no mean result of Comparative Anatomy 

 to have pointed out the analogy between the shark's skeleton and 

 that of the human embryo, in their histological conditions ; and 

 no doubt it is a very interesting one. But the perception of 

 such analogy is not incompatible with the endeavour to gain 

 insight into the purpose of the Creator, in so arresting the ordi- 

 nary course of osteogeny in the highly organised fish. No law of 

 human intelligence condemns it to restrict its cognizance of the 

 phenomenon, as solely those of an unfinished, incomplete stage of 

 an hypothetical serial developement of organic forms. 



The predaceous Sharks are the most active and vigorous of 

 fishes ; like birds of prey, they soar, as it were, in the upper 

 regions of their atmosphere, and, without any aid from a modified 

 respiratory apparatus, devoid of an air-bladder, they habitually 

 maintain themselves near the surface of the sea, by the action of 

 their large and muscular fins. The gristly skeleton is in pro- 

 spective harmony with this mode and sphere of life, and we shall 

 subsequently find as well-marked modifications of the digestive 

 and other systems of the shark, by which the body is rendered as 

 light, and the space which encroaches on the muscular system as 

 small, as might be compatible with those actions. Besides, light- 

 ness, toughness, and elasticity are the qualities of the skeleton 

 most essential to the shark : to yield to the contraction of the 

 lateral inflectors, and aid in the recoil, are the functions which the 

 spine is mainly required to fulfil in the act of locomotion, and to 

 which its alternating elastic balls of fluid, and semi-ossified bi- 

 concave vertebrne, so admirably adapt it. To have had their entire 

 skeleton consolidated and loaded with earthy matter would have 

 proved an encumbrance altogether at variance with the offices 

 which the Sharks are appointed to fulfil in the economy of the 

 great deep. 



I suspect that those who see in a modification of the skeleton, 

 so beautifully adapted to the exigencies of the highest organised 

 of fishes, nothing more than a foreshowing of the cartilaginous 

 condition of the reptilian embryo in an enormous tadpole, arrested 

 at an incomplete stage of typical developement, have been misled 

 by the common name given to the Plagiostomous fishes. The 

 animal basis of the shark's skeleton is not cartilage ; it is not that 

 consolidated jelly which forms the basis of the bones of higher 

 Vertebrates: it has more resemblance to mucus; it requires 1000 

 times its weight of boiling water for its solution, and is neither 



