384 EYCLESHYMER. [Vol. X. 



In the development of Amiurus a like phenomenon is 

 observed, although less marked, owing to the existence of rela- 

 tively less yolk. In the stage indicated in PI. XX, Fig. 15, the 

 embryo is well developed and in about the same stage as that 

 of Lophius just described, having almost reached the larval con- 

 dition. At the point where the tail of the embryo is attached 

 to the yolk there is a streak {g.r) extending ventrally to a 

 point considerably removed as indicated in the figure. This 

 is but faintly outlined in the unstained Q.g%, but by surface 

 staining it becomes strongly contrasted with the surrounding 

 surface. 



A section across this streak reveals the condition shown in 

 PI. XXI, Fig. 12. The periblastic layer is well defined and 

 the nuclei are aggregated in groups in such a manner that it 

 suggests a fusion of two portions. Lying above these two 

 groups are two corresponding thickenings of embryonic tissue 

 separated by a more or less distinct groove. In fact the entire 

 appearance of the section at once leads one to suspect that it 

 represents the fusion of two bands of embryonic tissue. I 

 interpret it as due to precisely the same process which we have 

 already noted in Lophius and which Miss Clapp has observed 

 in Batrachus, namely : The embryo differentiates so rapidly that 

 there is left behind a certain part of the germ-ring which never 

 enters into its formation. 



I believe this fact one of great importance in the conception 

 of the formation of the embryo, and to which I shall revert 

 presently. 



8. The Mesoblast in Fishes. 



I have endeavored to determine the origin of the mesoderm 

 in Amiurus, Lophius, and Coregonus, but as might be antici- 

 pated from the poorly differentiated condition of the cells of 

 the different layers, these forms, like other Teleosts, are unfav- 

 orable for deciding critical points. While the majority of 

 investigators first speak of the mesoblast when it is recogniz- 

 able as two lateral bands, there are others who have considered 

 it as primarily a continuous layer : Hoffmann ('8I), Kowalewsky 

 (•86), Mcintosh and Prince (-90), p. 728. 



