Miscellaneous. 67 



On the Structure and mode of Qrowth of the Scales of Fishes. 

 By Dr. Salbet. 



The author has made some investigations upon the structure of 

 the skin in fishes which must lead to great modifications in our ideas, 

 especially of the construction and growth of the scales. 



Fishes are generally sticky to the touch — a phenomenon which 

 M. L. Agassiz ascribed to a mucosity secreted by peculiar glands. 

 Leydig, however, showed that no mucus-gland exists at the surface 

 of a fish. The so-called mucosity is, in fact, only the most super- 

 ficial layer of the epidermis. In the terrestrial Vertebrata the most 

 superficial layers of the epidermis become hardened to form the 

 stratum corneum which scales ofi' at the surface. In fishes the 

 superficial cells of the epidermis, instead of hardening, absorb water, 

 become softer and softer, and constitute the mucous covering of the 

 surface, which is easily removed. The corium, placed immediately 

 beneath the epidermis, is formed essentially of two crossed systems 

 of connective bundles. It contains numerous pouches, in each of 

 which a scale is lodged. 



It is well known that the ctenoid and cycloid scales present 

 numerous concentric striae, which M. Agassiz interpreted as the 

 margins of superposed layers forming the scale. This opinion, 

 which is still generally accepted, is, however, quite erroneous, as 

 has been clearly shown by Dr. Salbey by means of vertical sections. 

 The striae are due to a series of irregular crests, which all belong to 

 the superficial layer of the scale. The deeper and much thicker 

 layer is formed by a series of superposed lamella) of two substances. 

 The thickest lamella) are colourless and brilliant ; the thinner ones 

 are yellowish and but slightly transparent ; the former are calca- 

 reous, the latter are composed of a sort of cement destitute of limc- 

 salts. The calcareous lamellae being generally thicker in old indi- 

 viduals than in the young, it is probable that their increase in 

 thickness is caused by a gradual incrustation of the interposed layers 

 of cement. The growth of the scale is explained by the fact, that 

 a deposit of calcareous salts is formed periodically in the part of the 

 corium which is directly applied against the lower surface of the 

 scale. This incrusted layer becomes for a time the lowest lamina 

 of the scale. Then a layer of cement is deposited between this cal- 

 careous lamina and the corium : this alternate formation of calcare- 

 ous and non-calcareous layers is repeated a great many times. 



Besides the concentric hues, the scales present striae which radi- 

 ate from the centre to the periphery. These are the " longitudinal 

 canals " of Mandl, the " fan-like furrows " of M. Agassiz, and the 

 " sutures " of M. Peters. The name proposed by M. Agassiz {sil- 

 lons en eventail) is perhaps the best, inasmuch as the stria; certainly 

 correspond to furrows of the surface. But from the bottom of these 

 furrows true partitions of unincrusted cement start, which traverse 

 the whole thickness of the scale and divide it into a certain number 

 of segments. By their partial incrustation these rays of cement 

 may assist in the widening of the scale. At the centre of the system 



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