610 J. T. PATTERSON 
Fig. 3 Outline reconstruction of the left half of specimen no. 257. The five 
sections from this specimen are illustrated in plate9. X 83. 
section passes through line ¢ to d of figure 3, and thus cuts 
across the angle lying between Embryos II and III. Finally 
figure 73 passes a little to the left of the center of Embryo IV, 
and shows the structure of that embryo. 
At the tips of the buds the cells are in active division (fig. 
30), indicating that the extension of the buds, during their early 
existence, is to be accounted for in this way. Their subsequent 
extension is due to other factors, which will be considered in 
the next sections. 
EXTENSION OF THE SECONDARY BUDS AND ORGANIZATION 
OF THE EMBRYOS 
The further extension of the secondary buds from the sides of 
the ectodermal vesicle very rapidly follows such conditions as we 
have described in connection with specimen No. 257. A rapid 
growth or increase in size of the vesicle also follows or accompanies 
this extension of the buds. Each bud grows down along the inner 
side of the wall of the vesicle, between the entoderm and the meso- 
