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 plate 9. X 83. 



section passes through line c 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- 



