663 



The facts exposed hitherto have had reference only to a great 

 and fundamental structural difference between two extensive groups 

 of osseous fishes. I may now add, that there exist also greater or 

 lesser structural discrepancies amongst the different tribes of each 

 group. But as this is not a suitable occasion for an exposition of 

 the details of this question, I will only say this much : In the higher 

 fishes, those with real osseous tissue, there exist differences, especially 

 with regard to iheform and size of the bone-corpuscles ; and I hope 

 to be able to show that there are peculiar and tolerably well cha- 

 racterized types of them amongst the Ganoids, Siluroids, Salmonida, 

 Cyprinoids, Clupeini, &c. In the second group there are more 

 varieties. In some tribes the bones are quite structureless homo- 

 geneous masses, as in the Leptocephalidce ; in others they have a 

 peculiar fibrous appearance, and consist of a singular mixture of 

 cartilage and osteoid structures, as Quekett first showed in the genera 

 Orthagoriscus and Lophius, to which I may add some Balistini ; but 

 in the great majority of the tribes of this group, the bones contain 

 peculiar tubes more or less similar to those of dentine. If these 

 tubes are well developed, the bones acquire a structure which can 

 in no way be distinguished from that of dentine, a fact, which also 

 did not escape the perspicacity of Quekett, who mentions its occur- 

 rence in the genus Fistularia, the Barracuda Pike (Sphyrcena bar- 

 racuda), and the Gar-fish (Belone vulgaris). I found the same 

 structure in many other genera of this group, especially among the 

 Plectognathi, Pharyngognathi, Sparidce, and Squamipennes ; but in 

 the greater number this tubular structure is not so well developed, 

 and is intermingled with more structureless parts. Another fact 

 deserving of mention with regard to the bones of this group is, that 

 there very frequently occur also structures, formed by the agglomera- 

 tion of calcareous globules of different sizes, which resemble in a re- 

 markable degree the lower layers of common fish-scales. 



My observations have also extended to the hard structures of the 

 skin of fishes, and of the rays of the fins ; and I may say that in 

 general the same laws, which apply to the structure of the endo- 

 skeleton, hold good also for the exoskeleton. Evidence of this is 

 especially afforded by the fins, the rays of which, independently of 

 their hard or soft condition, contain bone-corpuscles in all the tribes 

 where the internal bones are provided with them, whilst in the other 



