488 . STANLEY C. BALL 



The shell membrane is clearly visible, on one side closely 

 opposed to the yolk, while on the other a shrinkage space in- 

 tervenes. This capsule contained but one egg. That illus- 

 trated in text figure 4 shows the two ova at once. Only ex- 

 ceptionally do eggs lie so near the surface as indicated in figures 

 10 and 11 ; usually they are until late cleavage entirely surromided 

 by yolk. In figure 11 the plane passed through portions of 

 eleven yolk cells, of which there were, as determined by a count 

 of the visible nuclei, thirty-six originally enclosed in the capsule. 

 Hallez found from ninety to one hundred eighty-seven in vari- 

 ous capsules of P. cardii. As may be seen by referrmg to fig- 

 ure 10 of another section through the same capsule several 

 cells have already lost their membranes; only the degenerating 

 nuclei remain to indicate the number of cells. 



c. Behavior of the vitelline cells. Up to this point, with the 

 exception of the yolk nucleus above described, the structure and 

 behavior of the reproductive organs and their products are 

 remarkably similar in P. cardii and P. gemellipara. From here 

 on, however, the latter presents characteristic differences as to 

 the fate of the vitellarial yolk-cell nuclei, absorption of the yolk 

 and the formation of the ectoderm. 



The ectolecithal yolk cells in the P. cardii capsule, according 

 to Hallez, soon lose their membranes, those near the center 

 retaining them the longest. About one-half of their nuclei, 

 it is to be noted, degenerate, while the remainder come to lie 

 in the portion of the yolk which stains like cytoplasm. From 

 this portion the 'ergatoplasmic' granules of yolk have previously 

 separated and collected in 'balles vitellines.' This second form 

 of yolk stains distinctly with eosin. The cytoplasmic-like yolk 

 occupies the periphery of the capsule, sending a prominent 

 lamella inward between the embryos — ^now in process of segmen- 

 tation — and secondary ''parois alveolaires plus ou moins com- 

 pletes autour des masses eosinophiles." With its 'migratory' 

 nuclei the cytoplasmic yolk .stands as a syncytium siu-rounding 

 embryos and 'eosinophile' yolk. Hallez is of the opinion that 

 these migatory nuclei are effective in changing the nature of the 



