270 FISHES. 



calcareous particles arranged in a very compact manner : but this car- 

 tilage in the Lampreys never assumes this form of the covering, and in 

 the common Pride (cammoccetes) it continues always to be nearlj 

 membranous. 



The Sturgeon and Chimsera have, to a certain extent, the same sort 

 of softness of their spine as the Lampreys ; but the former genus has 

 many more bones in its head and shoulder, (at least one lamina 

 of their surface) perfectly hardened and bony. 



The other fishes present scarcely any other difference between them 

 except the hardness of the pieces composing their skeleton ; and it is 

 rather unfortunate that the fibro-cartilaginous group should have been 

 associated with the Chondropterygians by some naturalists. The 

 calcareous matter, — in other words, the phosphate of lime, is deposited 

 in the former, either in fibres, or in layers in the cartilage, which con- 

 stitutes the basis of their bones, just as it does in the most osseous of 

 the fishes. The only thing is, that it is less abundant in them, and 

 the tissue of the bone does not become so hard, neither does it assume 

 that homogeneity which characterizes the bones of certain osseous 

 fishes. 



As an example we may mention the Moon-fish (tetrodon mola) in 

 which we find some fibres, sprinkled, so to speak, over the mem- 

 branes. Lophius piscatorius is the fish that approaches the Moon-fish 

 most in softness. The other tetrodons, diodons, file-fishes, and ostra- 

 cions, have their bones both harder and more homogeneous, so that 

 they are distinguished from the real osseous fishes with very great 

 difficulty. 



It is also perfectly certain that the bony frame work of these fibro- 

 cartilaginous fishes is constructed on the same plan as that of the 

 osseous fishes, and not on that of the chondropterygians, and it is alto- 

 gether in opposition to truth for both Artedi and Linnaeus to deny to 

 these fishes both the ojiercula, and the branchiostegal rays : the file- 

 fishes have true ribs which are wanted in the tetrodons, the diodons, 

 and ostracions ; the real difference between the three genera being the 

 arrangement of their jaws respectively. The pipe-fishes (syngna- 

 thus) have not even this difference, but then they are deficient in the 

 ribs, and in the branchiostegal rays. 



A perfectly gratuitous assumption has been entertained as to the 

 bones of ordinary or osseous fishes being more flexible and extensible, 

 becomes a softer skeleton than the clases above them, and it has been 

 attempted to found on this doctrine a theory which pretends to ex- 

 plain the longevity observed in some species. Now, most of the 

 osseous fishes actually have their bones quite as hard, nay, harder than 

 other animals ; there are even some, in whose tissue we can discover 

 neither pores nor fibres, and which look perfectly homogeneous and 

 with a glassy polish to the eye. 



No fish whatever, either of the osseous or cartilaginous orders, 

 has epiphyses or medullary cavities in their bones ; but in some of 

 these animals, as the Trouts, the bony tissue is penetrated with a 

 variable quantity of oleaginous juice. Others, as the Dory, have the 

 internal parts of particular bones permanently cartilaginous, whilst 

 the surfaces of these bones are completely ossified In fine, we see 



