438 



MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 



percentage ot increase of wandering cells between Stages n and in is double that of the embry- 

 onic cells. Between Stages m and iv the increase per cent of wandering cells is less than that of 

 embryonic cells, and up to this time cell disintegration is ruled out as a disturbiu- factor 



aiv Fii;. 11, uinl fur details, see Table 



The second fact which was pointed out as characteristic of this stage, the distribution of the 

 yolk nuclei commensurate with that of the yolk itself, also points to the conclusion already r^hcd 

 This is well shown by two curves (Figs. 12, 13). In curve 13, which is constructed from a series 



... 



, b 6: 



F,,, 13._Curve abowins tl,. dlriritatfcn ,,f wa n ,leri n!t cells in Stage v, a. (v. Table ,., A, Anterior; P. Posierior. 



old reon * abundant in the thoracic-abdomiual. 



fold egion and in hat which answers to the future heart. We also notice the forward extension 



o he fuH ry CellS .' ey m ^ ant t rior ed * e of the oPe ^bes. In cut 12 the lateral extension 

 the nuclei on e.ther side the embijo is well shown. The mouth is involved in section No 28 



