4 SHARKS AND RAY-FISHES. 



skeleton most essential to the Shark; to yield to the contraction 

 of the lateral injectors and aid in the recoil are the functions 

 ■which the spine is mainlj required to fulfil in the act of 

 locomotion, and to which its alternating elastic balls of fluid, 

 and semi-ossified biconcave vertebrae so admirably adapt it. To 

 have had their entire skeleton consolidated and loaded with 

 earthy matter, would have been an incumbrance altogether at 

 variance with the offices which the Sharks are appointed to 

 fulfil in the economy of the great deep. 



Yet there are some who would shut out, by easily comprehended 

 but quite gratuitous systems of progressive transmutation and 

 self-creative forces, the soul-expanding appreciations of the final 

 purposes of the fecund varieties of the animal structures by 

 which we are drawn nearer to the Great First Cause. They see 

 nothing more in this modification of the skeleton, which is so 

 beautifully adapted to the exigencies of the highest organized 

 of fishes, than a foreshadowing of the cartilaginous condition of 

 the rej)tilian embryo in an enormous tadpole, arrested at an 

 incomplete state of typical development. But they have been 

 deceived by the common name given to the plagiostomous fishes: 

 the animal basis of the Shark's skeleton is not cartilasre: it is 

 not that consolidated jelly which forms the basis of the bones 

 of higher vertebrates : it has more resemblance to mucus ; it 

 requires a thousand times its weight of boiling water for its 

 solution, and is neither precipitated by infusion of galls, nor 

 yields any gelatine upon evaporation." (Lecture 6, Hunterian 

 Lectures, vol. li.) The bony frame of the Lampreys, on the 

 other hand, is little other than well-coagulated jelly, with no 

 more than about one and a half of earthy salts in its composition. 



Nor is it by the general likeness of shape, or internal structure 

 and physiology alone, that animals should have their relative 

 situation assigned to them in the order of nature. Separately 

 from these there are analogies also; and although these analogies 

 are chiefly judged of by the living actions of the races or indi- 

 vidual species — which actions, in the view of systematic writers, 

 whose business is principally with the dead animal, are of all 

 foundations of classification the least definite and trustworthv — 

 yet in their general bearing they serve important purposes in 

 one principal aim in the study of nature. In a work intended 

 to aid in the instruction of the public mind they should not be 



