AS AN INDEX OF AGE. 11 



periphery, but sutures are sometimes disposed concentrically (Ophidium, 

 Sudis, Rypticus, Heterotis, etc.). 



Peters denies the existence of osseous corpuscles in ordinary scales, but 

 admits the fact of their presence in Polypterus and Lepisosteus. 



In his paper on the embryology of the salmon, Vogt brings forward some 

 facts relating to the development of scales.* He states that the scales do not 

 show themselves till three months after hatching ; that the concentric plates, 

 so numerous in the scales of the adult salmon, are relatively few in number 

 in the young fish; but that the lines which indicate the borders of different 

 plates are just as continuous in the young as in the old scale, and thus in 

 no way indicate formation from isolated cells. lie notes that the central 

 focus is frequently smaller in the young as contrasted with the adult worn scale. 



Mliller issued a paper on Ganoids and natural classification of fishes. f In 

 part of this paper the author deals with some points relating to the taxonomic 

 value of the characters of scales. He held that the differences between the 

 scales of Cycloids and Ctenoids is of little importance, and can only be useful 

 for purposes of classification in a very limited way. | Later Vogt issued 

 another paper, § in Avhich he discusses the value of the characters of scales 

 in distinguishing different orders of Ganoids. 



In the Manual of Comparative Atiatomy, by Siebold and Stannius, || the 

 latter makes some statements regarding scales. He writes that scales cannot 

 be regarded as horny epidermic formations, and that it is impossible to ignore 

 the presence of a substance on the lower scale surface possessing a fibro- 

 cartilaginous texture and the existence of osseous corpuscles in some scales. 

 He does not admit that scale growth takes place only by means of super- 

 imposed layers, and regards it as doubtful whether it would be right to 

 take the different forms of scales exclusively as a basis for classification. 



In a paper by Dareste on the classification of Plectognathes, we find some 

 observations on the scales of fishes belonging to this order.^ In regard to the 

 integuments of Diodons and Tetrodons, he writes that in these we have not 

 scales, but spines, which are fixed in the skin by roots of a horny nature. The 

 spinous portion is very closely analogous to the ivory of teeth, and contains as 

 in these tubules which radiate out in all directions. The integument of 

 Triodons differs from that of Diodons and Tetrodons in possessing true scales, 

 comparable on the whole to those of osseous fishes. The external border shows 

 indentations similar to the ctenoid condition as described by Agassiz. The 

 cuirass of Ostracions results from the union of rhomboidal plates placed side 

 by side, and which possess an inferior layer of a horny nature and a superior 

 layer of osseous substance possessing calciferous tul)es Avhich recall the struc- 

 ture of teeth. 



Dareste, in another paper on Blochius longirostris** gives some considera- 

 tions on the value of scales as characters in classification. He would not 

 give them the role of dominating characters. 



Williamson pul)lished an important paper on the structure and develop- 

 ment of the scales and bones of fishes. ft Writing in 1873, Baudelot claims 



* Vogt, 1842. t Mlillcr, 1844. % MiiUer, 1843. § Vogt, 1845. 



II Siet)old and Stannius, 1849. II Dareste, 1850. 



** Dareste, 1850. ft Williamson, 1851. 



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