756 



MR. E. S. GOODRICH ON 



[Nov. 12,, 



to the peculiar dentine-like substance he discovered in " ganoid " 

 scales. Unfortunately he also applied it to a very different bony 

 tissue found in Lejndotus (p. 758). But in this paper the name 

 cosmine will be restricted to a tissue with canaliculi like those of 

 dentine, and the name " cosmoid " will be applied only to scales 

 with an outer layer like that of Megalichthys. 



The cosmine is restricted to that part of the outer surface of the 

 scale which is exposed. Those regions which are overlapped by 

 their neighbours in front have no cosmine, and are formed entirely 

 of the two lower bony layers, the vascular and the isopedine (text- 

 fig. 197, c). In both these are distributed numerous bone-cells.. 

 No such cells are found in the cosmine layer. The passage from 

 the one to the other is gradual. Overlying the whole cosmine- 

 covered surface is a thin layer of tiunsparent glassy appearance 

 and of homogeneous texture (text-fig. 197, A, & PI. XLIII. fig. 5).. 



(From Lankester's ' Treatise on Zoology,' by permission of Messrs. A. & C. Black.)! 



Scale of Megaliclithijs hibherti Ag. ; Carbonii'erous, England. A. Piece of a thick 

 transverse section, much enlarged. B. Section through the hind edge, en- 

 larged. C. Outer view of a scale, ae., anterior region covered hy next scale ; 

 c, large vascular cavity; cli., chamber of cosmine layer; dt., canaliculi of 

 cosmine ; g., thin outermost shiny layer ; h., irregular vascular canals ; i., bony 

 inner layer or isopedine; o., opening of chamber on surface; j)c., pulp-cavitj- 

 from which canaliculi radiate ; •y.c, vertical canal. 



Now, such a cosmoid scale grows at its edge and lower surface.. 

 New cavities may be excavated in the vascular layer, or old ones 

 filled up ; but the increase in bulk of the scale as it grows older 

 can only take place by the addition of new lamellse of isopedine 

 below, and by the deposition of substance, enclosing new chambeis 



