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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 (Triacanthus, Monacanthus, Aluteres, 

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

 Ephippus, Hcsmulon, 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 Spatularice ; they exist also in the fossil 

 Ganoids, as the excellent observations of Williamson have shown. 

 In many Ganoids, moreover, as Williamson 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 line in certain Cyprinoids 

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

 firm, and to add the following genera in which I find the same thing 

 to occur ; viz. Hydrocyon, Alepocephalus, Macrostoma, Bisso, Pia- 

 buca, Serrasalmo, Xiphorhamphus, Tetragonurus, Salminus, Chal- 

 cinus, Pygocentrus, Labeo, and Catostomus. But, besides the 

 instance of Sudis and certain Siluroids above referred to, I find that 

 many other Physostomi have true bone-corpuscles in their scales ; 

 not only those of the lateral line, but all of them. From the results 

 of my examinations up to this time, which, however, on account of 



