330 



A. RICHARDS AND JAMES T. THOMPSON. 



D 



TEXT FIG. A. Semidiagrammatic transection through the posterior of the 

 5o-hour embryo B' 23. The spots indicate the positions in which the greater 

 portion of the sex-cells are found at this stage. The rectangle includes the 

 area which is drawn in detail in Fig. 8. X 225. 



TEXT FIG. B. Transection from the iO5-hour embryo, showing the first 

 decided advance over the stage illustrated in Text Fig. A. Here the gut, 

 Wolffiau ducts and the ccelome have taken form. The rectangle includes the 

 area drawn in Figs. 14, 15 and 16. X 225. 



TEXT FIG. C. Showing progress of development after (5 days. Figs. 17 

 and 18 are detailed drawings of the area included in the rectangle. X 225. 



TEXT FIG. D. Transection through the developing gonads of the g-day 

 embryo, B 34. The sex-cells are collected ventral to the Wolffian ducts. The 

 dorsal mesentery shows a decided change from conditions found in earlier 

 stages. X 90. 



TEXT FIG. E. From the 1 3-day embryo B 42, showing the effect of the 

 developing swim bladder. X 90. 



