CYTOLOGY OF HYDRACTINIA AND PENNAKIA. 225 



in Figs. 1 5 and 19 and may have a stellate outline. It was prac- 

 tically impossible in Fig. 19 to determine whether there was a 

 fusion at this stage of the two nuclei or whether they were merely 

 in contact. 



Polyspennia. In Fig. 20, PI. IV., there are shown conditions 

 which seem to point strongly to polyspermia. The female pro- 

 nucleus is present and some distance away a single vesicle which 

 is similar in every respect to the male pro-nucleus of later stages. 

 The cytoplasm is indented just opposite as if modified by the 

 recent penetration of the sperm. Then close by this vesicle are 

 nine other vesicles, somewhat smaller but otherwise identical 

 with the single one. There is likewise the same modification of 

 the cytoplasm just opposite. The natural explanation seems to 

 be to regard these all as transformed sperm heads, and conse- 

 quently polyspermia. Fig. 21, PI. III., shows a second case of 

 probable polyspermia where there are three nuclei, one much 

 larger which is probably the female pro-nucleus. The other two 

 are interpreted as male pro-nuclei. That several nuclei may exist 

 previous to the first segmentation like this Fig. 21 and Fig. 48 of 

 Hargitt there can be no question and that they are in some in- 

 stances due to polyspermia I feel equally certain. But that this 

 is the exclusive interpretation I do not accept because nuclear 

 division may outrun cytoplasmic cleavage which results in giving 

 several nuclei in the cytoplasm as Figs. 43 and 43^ of Hargitt's 

 clearly indicate and I have confirmed. It seems more probable 

 that both explanations should be used in interpreting the mul- 

 tiple nuclear conditions. 



CLEAVAGE OF THE EGG IN Pennaria. 



This part of the paper on cleavage tends to show the manner 

 of cleavage rather than a detailed description of the process as 

 this has already been done by Hargitt. As was described in the 

 section on fertilization, the two pro-nuclei approach preparatory 

 to the first cleavage. Fig. 22, PI. II., shows the prophase of the 

 first cleavage. The female pro-nucleus has become much elon- 

 gated and there are distinct asters at each end. The spindle 

 fibers are just forming and the chromatin is still in the loose 

 stage ; the chromosomes are yet to form. The male pro-nucleus, 



