PLATE 6 



EXPLANATION OF FIGURES 



59 Median section, taken in a right-left plane, of specimen No. 256. The two 

 mesodermal vesicles have expanded until they now fill up the entire large extra- 

 embryonic cavity; but their adjacent walls still remain, forming a double-walled 

 partition between the cavities of the vesicles. X 95. 



60 Median section of specimen No. 247. It passes through plane a to 6 of figure 

 1. X 90. 



61 A section taken through plane c to d of figure 1 . X 90. 



672 



