1 86 CORA JIPSON BECKWITH. 



it seems to me, might account for Hargitt's interpretation of the 

 " nuclear nests." The rapidity of nuclear division is accom- 

 panied by slow cytoplasmic division so that the former constantly 

 outruns the latter, the result being that an unsegmented egg 

 often contains several such groups of vesicles or " nuclear nests." 

 In Clava the cytoplasmic cleavage does not lag so far behind 

 the nuclear division, but in fact keeps pace with it. For this 

 reason it was possible as shown by Figs. 14, 15, 16, 17, 18 and 19 

 to demonstrate the first cleavage spindle, and the successive pas- 

 sage of the two-cell stage into the four-cell, eight-cell and sixteen- 

 cell stages. The nuclear reconstruction takes place here again 

 by the formation of chromosomal vesicles ; but Clava differs from 

 Pennaria in that, as a rule, the vesicles all fuse into a single 

 nucleus between successive cleavages So far as I am able to 

 tell as yet, it seems probable that the cleavage in Clava is fairly 

 regular. 



SUMMARY. 



In the two hydroids (Pennaria and Clava leptostyla) under 

 question, the maturation and fertilization processes take place 

 in a perfectly typical fashion and form no exception to the gen- 

 eral rule in this regard. 



The conclusion that the " nuclear nests " indicate the forma- 

 tion of nuclei de novo is shown to be untenable. The occurrence 

 of these nests is explained by the conditions of nuclear recon- 

 struction after cleavage, the chromosomal vesicles failing to fuse 

 between successive divisions in Pennaria and the cytoplasmic 

 division lagging behind nuclear division gives a syncytium with 

 several nuclear groups. 



Maturation and the early cleavages take place by means of 

 mitosis and not amitosis. No evidence whatever of amitotic 

 division was found. 



My results regarding the maturation and fertilization phe- 

 nomena make it very probable that Hargitt's failure to observe 

 these stages was due simply to the fact that the eggs were not 

 obtained at the right time of day. In eggs collected at the 

 proper time (4-6 A. M.) there is no difficulty in proving the 

 typical stages of maturation and fertilization. 



VASSAR COLLEGE. 



POUGHKEEPSIE. N. Y. 



