508 PISCES FISHES. 



The spines of the common Stickleback (Gasterosteus) are indu- 

 bitable derivations from the cuticle ; but here they become fixed by 

 moveable articulations to the sides of the body, and are raised 

 or depressed by means of muscles inserted into their bases. Ad- 

 vancing one step further, we find in Silurus the first ray of the 

 pectoral fin, enormously developed and forming a strong serrated 

 weapon of a very formidable description, which, although both in 

 shape and structure exactly comparable to the spine upon the tail of 

 the Fire Flaire, are nevertheless connected by most beautiful and 

 perfect joints with the bones of the shoulder, so that they might 

 easily be regarded as forming pieces of the endoskeleton, did not 

 their peculiar structure indicate their real nature. 



We thus arrive at the important conclusion, that different por- 

 tions of the exoskeleton become approximated in character to those 

 of the endoskeleton, or in truth really convertible into true bone ; 

 and, with this fact before us, it becomes easy to understand the 

 nature of various parts of the skeleton of a fish, which upon any 

 other supposition would be not a little puzzling to the comparative 

 osteologist. 



The nature of the rays of the dorsal and anal fin of the Perch, 

 for example, together with the interspinous bones upon which they 

 are sustained, is quite unintelligible if they are regarded as belong- 

 ing to the endoskeleton ; and no dismemberments of the osseous 

 system as yet imagined, or supposed subdivisions of the vertebrae 

 into a greater number of elemental pieces than we have enume- 

 rated, has been able to solve the difficulty; but, if they are regarded 

 as ossified derivations from the exoskeleton^ all difficulties at once 

 vanish. 



Again, the opercular bones (28, 30, 32, 33) forming the gill- 

 covers of an osseous fish have been a fruitful source of discus- 

 sion, and M. Geoffroy St. Hilaire* was reduced to the necessity 

 of recognizing in these broad plates the ossicles of the human ear, 

 which, after dwindling to a rudiment in the descending scale of ver- 

 tebrate animals, suddenly reappeared in a new and exaggerated 

 form. " J'ai peu vu dans la srie des etres de ces resurrections 

 d'organes se remontrant subitement dans une classe apr&s avoir dis- 

 paru dans une ou deux de celles qui la precede dans Techelle," 

 are the impressive words of Cuvier upon a similar occasion ; and 

 it is certainly far more simple to imagine the epidermic plates 



* Philosophie Anatomique des pieces osseuses des organes respiratoires. 8vo. Paris, 

 1818. 



