TELEOLOGY OF THE SKELETON OF FISHES. 147 



The predaceons Sharks are the most active and vigorous of fishes ; 

 like the 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 them- 

 selves near the surface of the sea, by the actions of their large and 

 muscular fins. The gristly skeleton is in prospective 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 Avhich 

 encroaches on the muscular system as small, as miglit be compatible 

 with those actions. Besides, lightness, 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 tlie recoil, are the 

 functions wliich 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 vertebra?, so admirably adapt it. To have 

 had their entire skeleton consolidated and loaded with earthy matter 

 would have been an encumbi-ance altogether at vai'iance 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 pur- 

 poses 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 organised of fishes, than a foreshowing 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 Plagio- 

 stomous 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 

 precipitated by infusion of galls, nor yields any gelatine upon 

 evaporation. 



In like manner the modifications of the dermal skeleton of fishes 

 have been viewed too exclusively in a retrospective rehition with the 

 prevalent character of the skeleton of the Invertebrate animals. 

 Doubtless it is in the lowest class of Vertebrata that the examples of 

 great and exclusive development of the exo-skeleton are most nume- 

 rous ; but some anatomists, in tlieir zeal to trace the serial progression 

 of animal forms, seem to have lost sight of all the vertebrate instances 



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