Prof. KoUiker on the minute Structure of the Bones of Fishes. 73 



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

 in no loay 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)y and the Gar-fish {Belone vulgaris). I found the same 

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

 Plectognathiy 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 

 case these rays are formed of a homogeneous osteoid substance or of 

 a tubular structure, which may also in some fishes, as Williamson 

 first showed in the Ostracionts, assume the structure of real dentine, 

 as in many Plectognaths {TriacanthuSy Monacanthus, Aluteres, 

 Tetraodon, and others), and in certain Acanthopterygii (Equula, 

 Ephippus, HcBmulon, Pristipoma, Scatophagus, Centrarchus) . With 

 regard to the skin, we may at least go so far as to say that in no fish 

 whose endoskeleton is destitute of bone-corpuscles do they exist in 

 the hard structures of the skin ; but, on the other hand, the tribes 

 which have real osseous tissue do not all present it also in the skin. 

 Scales or plates with bone-corpuscles are found amongst living 

 Ganoids, e. g. in Polypterus, Lepidosteus, and even Amia (in whose 

 scales J. Miiller erroneously supposed them to be wanting), and also 

 in the Acipenserini and Spatularioi ; they exist also in the fossil 

 Ganoids, as the excellent observations of Williamson have shown. 



In many Ganoids, moreover, as Wilhamson and Quekett have 

 shown, the scales often contain dentinal tubes, or even portions of 

 real dentine (" Kosmine " of Williamson) amidst true bone. In 

 the scales of Lepidosiren, also, I find bone-corpuscles, but mostly fusi- 

 form, and only here and there having a simple stellate figure. Of 

 the other fishes which have bone-corpuscles in their skeleton, little 

 has hitherto been noted as to the coexistence of such corpuscles in 

 their scales, but I find it to prevail to a considerable extent among 

 them. The presence of bone-corpuscles has been long known, it is 

 true, in the larger scales of the *' corselet" of Thynnus, also in the 

 dermal plates of certain Siluroids (Loricaria and Callichthys), and 

 was pointed out by J. Miiller in the scales of Sudis. Ley dig, too, 

 states that true bone-corpuscles exist in the walls of the grooves and 

 semicanals upon the scales of the lateral Hne in certain Cyprinoids 

 (Carp, Tench, and Barbel). This statement I am able fully to con- 



