hargitt: pennaria tiarella and tubularia crocea. 207 



Addendum. 



Since this paper was written there has appeared a short paper by 

 Cora Beckwith ( :09) on the early history of the egg of Pennaria tiarella 

 and Clava leptostyla. Beckwith finds that in both species polar cells 

 are formed by a process of mitosis, which is in agreement with my 

 results on Pennaria and Tubularia. She finds, however, that this 

 takes place between the hours of 4 and 6 in the morning, a condition 

 not in agreement with my observations, since I found that eggs of 

 Pennaria which were killed at 6 A. M., and later, possessed the germi- 

 native vesicles; and only near the time of liberation of the medusa 

 (about 7 P. M.) were maturation spindles and polar cells to be observed. 

 This seems to show a considerable variation in the time of the comple- 

 tion of the maturation process. 



Our results in regard to the fate of the nucleolus are also not in 

 agreement, Beckwith finding that this body is cast into the cytoplasm, 

 while I always found that it disappeared within the germinative 

 vesicle before the dissolution of the nuclear membrane. Beckwith 

 observed in Pennaria the fusion of the germ nuclei, and I, too, found 

 this to occur, though apparently these nuclei may sometimes be sepa- 

 rate, at the time of the formation of the first cleavage spindle. The 

 formation of chromosomal vesicles, which often persist, and the delay 

 of the segmentation of the cytoplasm in the cleavage of Pennaria, are 

 observations which I can confirm. 



