GERMINAL LOCALIZATION IN THE EGG OF CEREBRATULUS. 29 



In treating eggs with Ca-free sea-water after the egg mem- 

 brane "was shaken off (which can be done far more readily in the 

 nemertine egg than in that of the sea-urchin.), I obtained two 

 kinds of embryos, (a) ring-embryos, i. e., eight blastoraeres, 

 arranged in a ring, and (b) plate-embryos, i. e., eight blastomeres 

 arranged in one or two rows (Yatsu '10 pp. 9,-10). These 

 embryos were put back into ordinary sea-water and allowed to 

 develop further. I obtained seventeen pilidia, thirteen from the 

 ring-embryos and four from the plate-embryos. 



In some the apical organ did not develop at all (Fig. 24 A, 

 D, G ; Fig. 25 A, C, D), while in others it was multiple (Fig. 

 24 B, C, E). In some the gut was double (Fig. 24 G ; Fig. 25 



Fig. 25. 



A, pilidium arising from a plate-embryo a. Notice that the eight blasto- 

 meres were arranged in a row ; when sketched, they had divided once 

 (16-cell stage) ; C and D, larvje from plate-embryos of C. marginatus. 



