120 Dr L. Mandl on the Scales of Fishes. 



With regard to the longitudinal canals, M. Agassiz calls 

 them furrows. " There are grooves at the margin of their 

 outer surface, which correspond to each other in the different 

 leaflets, and multiply durmg the growth of the scale." In de- 

 scribing the different external forms which the contoru" of scales 

 presents to the naked eye, M. Agassiz likewise mentions the 

 lobes, and continues thus : " When these lobes are hardened 

 in the form of small teeth or very sharp serratures, and are 

 only fomid in the last leaflet (the preceding successively dis- 

 appearing as th^ become blunter), scales are then produced 

 having a simple serrated edge ; but when they' are found on 

 many consecutive leaflets, the edge of the scale is covered 

 with numerous rows of points, and it is then very rough to 

 the touch." 



We shall afterwards see that our explanation of these points 

 differs materially from that given by M. Agassiz ; that we 

 find them to be distinctly organized formations, composed of 

 an envelope and a dentiform body, which presents roots, dif- 

 ferent sui'faces, many degrees of development according to 

 position, and different fonns in different families of fishes. 



Lastly, M. Agassiz establishes the principal divisions of the 

 class of fishes according to the form of the scales. " I believe 

 that I have found," he says, " in the differences presented by 

 scales, a means of tracing more exactly the natural affinities 

 of all kinds of fishes. It cannot at least be disputed that the 

 animals of this class possess, in their scaly integuments, a cha- 

 racter peculiar to themselves, and not found to exist in any 

 other class. The following ai'e the orders and the names of 

 the pi'incipal families : 1st Order : The Placoides. — Thus 

 named on account of the irregularity of the solid parts of their 

 integuments ; these consist of masses of enamel, often of con- 

 siderable dimensions, at other times reduced to small points, 

 such as the rings of the rays and the different shagreened sur- 

 faces of rays and sharks. 2d Order : The Ganoides. — The cha- 

 racter common to all these is the angular form of the scales, 

 which are composed of two substances, namely, corneous or os- 

 seous leaflets placed one above another, and covered with a thick 

 layer of enamel. M. Agassiz includes many families both recent 

 and fossil in this order, such as the Sclerodermes, Gymnodon- 



