DEVELOPMENT OF THE SCALES AND BONES OF FISHES. 
645 
granules which are formed within the fibrous tissues of his inferior layers, and con- 
ceiving them to be cells, has built upon them the hypothesis just quoted. 
The publication of this memoir, controverting as it did, some of the opinions of 
M. Agassiz, elicited from that distinguished Ichthyologist an elaborate reply which 
was published in vol. xiv. of the same journal. He then considered that each scale 
consisted of but one substance, and that the existence of two layers, except in certain 
cases, was an error*. 
Subsequently, however, M. Agassiz discovered his own error on this point, and 
became convinced that each of these scales did really contain two different structures. 
In his great work on fossil fish, whilst correctly pointing out the non-existence of the 
longitudinal canals of M. Mandl, which he considers to be merely grooves in the 
upper layer, he observes, “ On se convaince alors que chaque ficaille de Cycloide est 
formee de deux couches distinctes et superposees, qui toutes deux sont lamelleuses, 
mais dont le plan de stratification est different, la couche interne etant continuee 
entiere, tandis, que la couche externe, qui seule inontre des lignes concentriques et 
une grande partie des sillons, est souvent interrompue.” Still, however, denying the 
existence of fibres in the lower layers, which he says are transparent, sometimes 
yellowish, never containing cells or corpuscles, and are softened by maceration, he 
proceeds to describe what he believes to be the structure of the upper layer. “ Au 
dessus de cette couche se trouve une seconde couche qui porte en elle les conditions 
des ornemens de Fecaiile. La substance de cette couche est plus dure, plus cassante 
et plus transparente que celle de la couche inf^rieure ; elle n’a jamais cette teinte 
jaunatre, et dans la plupart des cas, on n’y distingue aucune structure particuliere. 
Dans les ecailles minces c’est comme un vernis seche et racorni, dont on aurait 
convert la superficie de fecaiile. Mais dans les ecailles epaisses des Labres, on 
aperqoit distinctement sur les coupes verticales, des traces de stratification, mais d’une 
stratification discordante avec celle de la couche inferieure. Le plan des lames ne 
repond pas a celui de fecaiile tout entiere, mais elles sont couchees fune sur fautre 
comme les tuiles d’un toit, et plus ou moins imbriquees'|~.” With reference to the 
corpuscles of M. Mandl, he observes, “ Les corpuscules, qui dit on, forment une 
couche particuliere au milieu de fecaiile, se voient, il est vrai, assez souvent, sous la 
forme d’ovales ou de carres a contours ombres et indistinctement limites;” but he 
doubts their being true corpuscles, and rather refers the appearance to some solution 
of continuity between the upper and lower tissues j: : the latter of these tissues he con- 
ceives to be not fibrous, but of a horny texture, and an exuded- secretion from the sac 
into which he considers the lower and anterior portions of the scale to be fitted. After 
pointing out the resemblance that exists between the scales of Cycloids and Ctenoids, 
M. Agassiz goes on to give his interpretation of the nature of the peculiar teeth in 
the margin of the scales of the latter order. In some, which have only one marginal 
row of teeth, as Corniger and Myripristis, he thinks that “ ce sont tout simplement des 
* Ut supra, vol. xiv. pp. 104, 105. f Poissons Fossiles, vol. i. p. 70. + Idem, p. 72. 
MDCCCLI. 4 o 
