HARGITT: PENNARIA TIARELLA AND TUBULARIA CROCEA. 175 
was seen, though this may not be remarkable, since the region is 
discernible only by a slight difference in the staining reaction. Since 
an aster seems not always to accompany the spermatozoon, it cannot 
be definitely determined whether there is a rotation of the sperm 
during its migration, though when present the aster is sometimes at 
the deeper side of the spermatozodn. Even when this is the case no 
angle is found in the ‘‘path” (Fig. 17a). 
Usually the sperm head penetrates the egg only a short distance 
before it begins its transformation .into the sperm nucleus, for one 
finds the latter in its early stages not far removed from the periphery 
of the egg (Figs. 18, 19b, 19¢). ‘This is characteristic and appears to 
occur in all cases except where supernumerary spermatozoa enter the 
egg, in which case the extra spermatozoa remain unchanged for some 
time. After the entrance of the spermatozo6n there is often an entire 
absence of asters in connection with the germ nuclei; this makes it 
impossible to distinguish the egg nucleus from the sperm nucleus, 
or to learn exactly what transpires before they conjugate. 
Figure 16a represents the sperm nucleus, and Figure 16b the egg 
nucleus of the same egg, both being near the surface of the egg. Be- 
tween the surface and the sperm nucleus. there can be traced in the 
sections an ill defined “entrance track.’”’ he nucleus itself has a 
definite aster, the rays of which centre in a large clear area, in which, 
however, no central body is found. ‘This area is on the side of the 
nucleus opposite to that which faces the egg nucleus; however, a second 
very faint and indefinite series of radiations seems to exist on this side 
also. The sperm nucleus (Fig. 16a) is smaller than the egg nucleus 
‘(Fig. 16b) and spherical, while the latter is ellipsoidal and is not 
accompanied by any radiations. Each’ nucleus is composed of a 
single vesicle, and the chromatin is incorporated in a linin reticulum; 
it is more concentrated in the sperm nucleus. In this egg it is perfectly 
clear that the sperm nucleus possesses an aster and the egg nucleus 
none, though the aster is on the side opposite the egg nucleus, instead 
of the one facing it, as commonly occurs in the sperm nucleus of most 
animals. Perhaps a rotation of the sperm nucleus is yet to take place. 
Figures 21a, 21b (Plate 3) represent the germ nuclei of another egg. 
These are close to each other, and not far from the surface of the egg. 
While one (Fig. 21a) is distinctly lobed, as though it had resulted from 
the fusion of a number of vesicles, the other (Fig. 21b) shows still more 
plainly that it has been produced by the confluence — not yet com- 
pleted — of several separate vesicles. A fairly conspicuous, and 
even-meshed network fills out each of the nuclei; but the chromatin 
