492 STANLEY C. BALL 



is very similar to that in the vitellaria. Since in hving yolk 

 all particles exist as either spherical, oval or oblong granules 

 (figs. 12, 15) it is probable that the flakes present in preserved 

 material are globules exploded by the action of reagents. 



The nuclei of the cells shown in figure 11, whose membranes 

 still remain intact, are already beginning to disintegrate. Suc- 

 ceeding stages of degenerating yolk-cell nuclei appear through- 

 out this section as well as that represented in figure 10. 



Occasionally individual yolk cells, perhaps endowed with 

 unusual vitality, retain the membrane until late cleavage in 

 the condition presented when the cell was enclosed in the capsule. 



3. Maturation and fertilization 



a. Insemination. That the egg in P. gemellipara may be 

 entered by the spermatozoon immediately after leaving the 

 ovary is plainly indicated in figure 9. which shows several sper- 

 matozoa between the two eggs and surrounding yolk cells. A 

 careful search through all the sections of these ova yields no 

 evidence that either one has been penetrated. 



Each egg of another capsule, illustrated by text figure 4, 

 about which the shell membrane had been formed, contains 

 a spermatozoon. Either insemination has just taken place or 

 the spermatozoon remains quiescent for some time before form- 

 ing the male pronucleus, for both of these show plainly the 

 long, deeply-stained head and a delicate coiled flagellum. 



Without doubt many spermatozoa become enclosed in each 

 capsule, where, as Patterson points out, their identity becomes 

 obscured by the yolk granules. Occasionally a mass of sperm 

 occupies a vacuole in the yolk; such a condition is shown in 

 text figure 5. Presumably the sperm cells continue active in 

 the capsule for some time, so that any egg that is not inseminated 

 at the time it enters the capsule may later encounter the sperm. 



Several other eggs have been observed in which the male 

 pronucleus had become lobulated or amoeboid in shape, and 

 had approached, in some a lesser and in others a greater dis- 

 tance toward the female element (text fig. 7). 



