422 TEGUMENTARY ORGANS 



into their composition, as we find to be the case in the scales of the 

 Ganoids (Miiller), and in the truly bony semi-canals which are 

 attached to the scales of the lateral lines of many fishes." ^ 



For the details of the various modes in which Ganoin, true osseous 

 tissue, and those varieties of tubular, more or less dentine-like 

 tissues, to which Prof Williamson has given the names of " Lepidine 

 and Kosmine," are combined together in the scales of Ganoid and 

 Flaccid fish, I must refer to that gentleman's memoirs, already so 

 often cited. 



In the Ctenoid and Cycloid fishes there is a superficial " Ganoin " 

 layer composed of numerous thin structureless calcified laminee, which 

 are frequently thrown into folds, papilla; or spines. The deeper 

 substance of the scale is composed of a series of layers of a mem- 

 branous substance, each layer being composed of parallel fibres 

 which take a different direction from those of the superficial and 

 subsequent layers, so that the fibres of alternate layers cross 

 diagonally. No endoplasts or cells are ever distinguishable among 

 the fibres. In the deepest part of the scale these layers are entirely 

 membranous : but in passing towards the surface, minute lenticular 

 masses of calcareous matter make their appearance in the membranous 

 substance. As Prof Williamson justly states, these lenticular bodies 

 are not developed between the membranous fibres and lamelliE, but 

 in them : " they commence as a small calcareous atom, and increase 

 in size by the external addition of new concentric laminse ; the 

 direction of the latter not being parallel with, or having any reference 

 to, that of the lamina; of fibrous membrane with which they so 

 amalgamate ; thus they are not depositions from, but growths in the 

 membrane ; which growths, as they increase in size, retain their 

 primitive tendency to assume a lenticular form." Following the layers 

 of the scale outwards, these isolated calcareous deposits not only 

 enlarge, but ultimately become fused together, forming at length 

 either a continuous calcareous mass in each layer, or presenting 

 fissures which in some cases traverse the original lenticular calcareous 

 deposits, in others are interstitial to them. I think one cannot but be 

 struck with the complete analogy between the structure and mode of 

 development here described and those which I have previously shown 

 to obtain in the calcified tegumentary organs of the MoUusca and 

 Crustacea. The ganoin layer corresponds very closely with the 

 " epidermis " of the shell or test ; the middle laminated calcified 

 substance is formed by the fusion of concentrically laminated con- 

 cretions deposited in a membranous matrix in the Fish, the Mollusk, 



^ Leydig ; Rochen und Haie, 1852. 



