294 E. E. JUST 
As the head is drawn into the egg, the inner bulb turns with 
its growth. Finally, the portion forming the external bulb is 
engulfed. ‘The middle piece and tail, asin Nereis, never enter 
the egg (fig. 17). They may often be found in sections out- 
side the membrane after penetration of the sperm head (see 
figures). 
I have never found the spermatozoon in the Nereis or in the 
Platynereis egg at the time or in the form figured by Wilson 
(96 and ’00). 
Does the sperm head rotate? I could not positively determine 
the rotation of the sperm head in the egg of Platynereis. In 
the first place, a definite cone organ, like that of Nereis, is lack- 
ing, and secondly, the middle-piece does not enter the egg. 
The history of the sperm penetration is known practically for 
every minute from entrance to pronuclear copulation. Meves’ 
fixation alone was not depended upon. The Bouin preparations 
gave results much like those of Bonnevie’s with picro-acetic 
mixtures on the Nereis eggs. While absolutely worthless for 
cytoplasmic detail, they were helpful in determining the struc- 
ture of the sperm nucleus after penetration. The evidence 
favors rotation; the turning of. the inner sperm bulb (fig. 17) 
and the position of the long axis of the sperm and aster as often 
found at right angles to the radius of the egg (fig. 22). 
The sperm aster does not arise until the nucleus is beyond 
the yolk region (figs. 14 to 22). Within the endoplasm, the aster 
once formed, quickly divides equally, but the amphiaster does 
not long retain its equal poles, for one sperm centrosome and its 
aster gradually dwindle in size. Rays arise between one or both 
of the sperm centrosomes and the inner centrosome of the matura- 
tion spindle, thus forming a secondary spindle. The sperm 
nucleus lies nearer the larger sperm centrosome (see figs. 20 to 25). 
3. Copulation of the germ nucler. The egg chromosomes, after 
the formation of the second polar body, form fourteen chromo- 
some vesicles which fuse to establish the egg nucleus (figs. 26, 27), 
all vestiges of the egg aster disappearing. ‘The sperm nucleus 
enlarges as its asters become smaller. At the time of apposition, 
but one sperm aster is found (fig. 28). I believe that one sperm 
