CHONDROPTERYGII. 



35 



dropterygii, whatever of osseous matter, or earthy 

 salts, is funned in the cartilaginous matter, forms in 

 grains, which are detached from each other without 

 any appearance of being organised in any direction. 



The bones, even of those animals which have the 

 skeleton hardest and most perfect when mature, are 

 cartilaginous when they are young, and they ossify 

 gradually, requiring a longer or shorter time in dif- 

 ferent races of animals ; but, when ossification begins, 

 always begins at points, and proceeds from those 

 points as centres, in lines of definite arrangement, the 

 characters of which are worthy of more attention than 

 they have hitherto received. Thus there is in the 

 cartilage of these animals, a principle by means of 

 which it can organise the earthy parts of the bone, as 

 well as produce them, whereas, in the fishes under con- 

 sideration, this principle seems to be entirely wanting ; 

 and therefore, though the general cartilaginous basis 

 of the bone may be considered as a product of organi- 

 sation, the hard matter which may afterwards be 

 imbedded in it, is not so imbedded in consequence of 

 any particular law of organisation. In this respect 

 therefore, we may with perfect correctness say, that 

 these fishes are a stage lower in the structure of their 

 bones than any other verteb rated animals. It seems 

 also that their cartilage is differently formed. The car- 

 tilage of the others is to a considerable extent fibrous, 

 though the fibres are not easily perceptible, in conse- 

 quence of the closeness of their union ; and we may 

 suppose that the reason why the bony matter in this 

 sub-class of fishes is not organically arranged, is the 

 absence of this structure in the cartilaginous basis. 

 Therefore, though the term "cartilaginous" answers 

 very well for distinguishing them from other fishes, 

 we must not suppose that they have the same kind 

 of cartilage as the others only without the bony mat- 

 ter in it ; for their cartilage is not only really but 

 necessarily different. If it were the same in substance 

 and in arrangement, it would be impossible not to 

 suppose that it would ultimately ossify into the very 

 same kind of bone. If we were not to conclude that 

 the same preparing substance would, and must, under 

 the same circumstances, produce the very same 

 result, then we could come to no conclusion what- 

 ever, and there would be an end to natural history 

 as a science. 



Imperfect as the bony structure of these fishes thus 

 seems, it has its advantages. They move more freely 

 than animals with stiff bones ; they are much less 

 liable to injury ; and so far as we know, they are 

 exempted from old age, from decay, and probably 

 from death, except by casualty. 



In all cases where the bones of the vertebral co- 

 lumn are stiff, the motion of the joints is confined to 

 certain directions only ; and though some vertebrated 

 portions, as in the necks of many birds, and more 

 especially in the chelonia, which have hard shells, 

 have very beautifully formed joints, and admit of a 

 wonderful degree of flexure, yet in them the flexure 

 is produced by every different joint being bent in a 

 different direction, there being as many centres of 

 motion as there are joints, and consequently a very 

 complicated apparatus of muscles for moving them. 

 The bones of the true serpents (we are of course 

 speaking of the vertebral column only), and those of 

 bony fishes, afford instances of motion which is more 

 free and more general in its direction ; but still the 

 principal motion is referable to a definite plane in 

 the clody of the animal. That of the serpents is 



vertical, passing through the middle of the back and 

 the belly, and there is generally a distinct mesial 

 line along one or both. The bony fishes again are 

 articulated, so as to have their principal motion in 

 the horizontal plane passing through the middle of 

 the sides, which are generally marked by lateral lines. 

 The joints in these are without processes, upon 

 which a particular motion can be performed as on a 

 centre, for they consist of two hollow conical cups, 

 with their lips applied to each other, and their cavi- 

 ties filled with cartilaginous substance, so that each 

 of them may be considered more or less as a universal 

 joint, though this is modified in different species, in 

 such a manner as best adapts them to their habits ; 

 a bone of this kind is obedient to the action of the 

 general muscular mass in which it is embodied, and 

 does not need detached muscles for the motion of 

 every single joint, attached at each extremity to one 

 of the bones which meet at the joint, in the same 

 manner as in animals which have the bones articu- 

 lated upon each other by means of processes and 

 cavities. The muscles of fishes act between the bone 

 and the skin, as their two principal points of inser- 

 tion ; and as the skin is supported externally by the 

 weight of the element in which the fish moves, much 

 less muscular exertion is required to produce motion, 

 than in animals which have the bones with regular 

 joints. 



In the cartilaginous fishes, this facility of motion is 

 communicated to the whole of the vertebral column, 

 so that they can move with still less of muscular 

 effort than the true fishes. Thus they have great 

 command of themselves in the water, without much 

 exhaustion of their system ; and as there is at the 

 same time no positive limit to the growth of their 

 bones, they are exempted from old age and decay. 



This leads us to another peculiarity of their struc- 

 ture, their respiratory system. The quantity is 

 proportionately less than that of bony fishes, and 

 their breathing apparatus is of more simple structure. 

 In consequence of this, the whole functions of life in 

 them are carried on with less exhaustion of the sys- 

 tem than those of the other fishes ; and thus, while 

 their body is less worn by the operation of living, it 

 requires less renovation, the principle of life in it is 

 more durable, they can bear abstinence for a greater 

 length of time, can feed more voraciously when they 

 do feed, and more of the substance of their food can 

 go to the increase of their size. These particulars 

 vary much in the different divisions or orders into 

 which they may be divided, and also in the subdivi- 

 sions, but still they, to some extent, apply to the 

 whole. 



There is this further to be remarked on them gene- 

 rally, that their organs and manner of reproduction 

 are much more perfect than those of the other fishes, 

 that in these respects they bear a considerable resem- 

 blance to reptiles ; and some of them have even a 

 physiological, though not a structural, resemblance 

 to the marsupial mammalia. In describing them 

 according to their feeding apparatus, which, however, 

 is much less satisfactory in the case of fishes than in 

 that of any other vertebrated animals, the most re- 

 markable circumstances are the absence of maxillary 

 and intermaxillary bones for supporting the teeth. 

 But the teeth, though they are without bony sup- 

 ports, are not the less powerful ; for some of these 

 fishes, as the shark for instance, have more formidable 

 mouths than any other animals. The teeth are 

 . C a 



