4 
SHARKS AND RAT-FISHES. 
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 biconcave vertebrse 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 reptilian embryo in an enormous tadpole, arrested at an 
incomplete stage 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 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 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. ii.) 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 tne least definite and trustworthy — 
yet in their general bearing they 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 
