EARLY HISTORY OF EGG OF HYDROIDS. 185 



demonstrate the maturation processes and that they take place 

 with the utmost exactness and in the typical manner, as reference 

 to the figures will show. Fig. i shows the germinal vesicle of an 

 egg of Pennaria in which the inner wall is breaking down, the 

 nucleolus passing into the cytoplasm where it is lost, while the 

 chromatin is grouping itself around the periphery of the nucleus 

 to form the chromosomes. Figs. 2 and 1 1 are nearly correspond- 

 ing stages of the first polar spindle in Pennaria and Clava lepto- 

 styla respectively. In both forms the chromosomes are evidently 

 bipartite and the number is determined to be one half the somatic 

 number. In the figure of Pennaria (which is in the late pro- 

 phase) the spindle has not yet swung around into position. A 

 comparison of Figs. 3 and 12 shows again practically identical 

 conditions of the second polar spindle in the two forms. The 

 first polar body lies outside the egg, the second polar spindle is 

 in the late anaphase. I have found numerous intermediate 

 stages. Figs. 4 and 13 show corresponding stages of the recon- 

 structed egg nucleus with the polar bodies lying outside the egg. 



Figs. 5 and 6 give two stages in the fertilization of Pennaria. 

 The two-germ nuclei lying side by side at the periphery of the 

 egg later move toward the center of the egg where they form the 

 fusion nucleus at the ends of which astral radiations appear. 

 The origin of the first cleavage spindle is not determined. For 

 lack of proper stages the fusion of the two-germ nuclei has not 

 been demonstrated with certainty in Clava leptostyla. 



From this point forward the two forms differ slightly. In 

 Pennaria, after the first cleavage the two nuclei are reconstructed 

 by the formation of chromosomal vesicles as shown in Figs. 7 

 and 8. For some reason, possibly the rapidity of nuclear divi- 

 sions, the chromosomal vesicles often fail to fuse into a single 

 nucleus but give rise to a " nuclear nest " which subsequently 

 gives rise directly to the chromosomes of the following cleavage 

 figure. Fig. 9 shows two such vesicles passing on to a spindle, 

 one vesicle already broken up into the individual chromosomes, 

 the other still in the vesicular stage. Fig. 10 shows an equatorial 

 view of such a group of vesicles, some of the chromosomes 

 already forming an equatorial plate. 



A shortening of the resting stage between the nuclear divisions, 



