DEVELOPMENT OF PARA VORTEX GEMELLIPARA 495 



spermatozoon, and upon the number and position of the chromo- 

 somes, than upon the shape of the latter. 



The egg at the left in the capsule in text figure 4 has extruded 

 no polar bodies, contains a spermatozoon and the chromosomes 

 are just being drawn from the disappearing germinal vesicle. 

 Its mate agrees with it in the first two particulars, but shows 

 an advance in that eight small masses of chromatin, which I 

 conclude to be diads, are present in the spindle; in other words, 

 the cell is in the early metaphase. Text figure 8 pictures a 

 similar condition, except that it is impossible to distinguish all 

 the chromosomes. One centrosphere has already divided, 

 while the other is in the process of division. 



Hallez ('09) determined that sixteen 'caryomerites' are pres- 

 ent in the first polar spindle of the egg of P. cardi. Eight of 

 these are eliminated in the first polar body. The second mat- 

 uration spindle contains, as he expresses it, "four chromosomes 

 (= eight caryomerites), half of which enter the second polar 

 body." 



My material yielded but a single instance where the first 

 polar body had been given off, and the second maturation spindle 

 was forming. In this egg (fig. 9) the first polar body, not quite 

 detached, has already begun to degenerate, as indicated by the 

 scattered chromatin. The centrosome remaining in the egg 

 has divided to form the second polar spindle whose fibers are 

 drawing the four diads toward the equatorial plate. Another 

 section contains the spermatozoon which has begun to enlarge 

 to form the male pronucleus. 



In the preparation which best shows the first and second 

 polar bodies the capsule was sectioned in such a plane that 

 portions of the second polar body, though still connected with 

 the egg by a protoplasmic bridge, lie within two of the serial 

 sections, neither of which passes through the egg itself. A third 

 section, however, contains a thin tangential portion of the 

 egg showing the female pronucleus with small masses of chroma- 

 tin. Text figure 6 represents a reconstruction of this capsule. 

 The female pronucleus is lying just inside the vitelline mem- 

 brane in the animal pole of the egg. Lobule formation has 

 again set in. 



