a 
HARGITT: PENNARIA TIARELLA AND TUBULARIA CROCEA. 177 
additional reason for the conclusion that the aster, when present, 
owes its origin to the spermatozoén, though it seems as though the egg 
nucleus in some cases (Fig. 21b) possessed an aster, and the sperm 
nucleus none. Figure 17a represents a spermatozo6n which has re- 
cently entered an egg. A cone is found at the surface of the egg, and 
there is a funnel-shaped region in the cytoplasm between the surface 
and the spermatozoén. In front of the sperm is an aster with no 
visible centrosome. ‘T'wo other spermatozoa had penetrated the egg, 
but these remained in the most superficial layer of the cytoplasm, 
and showed no signs of migration. ‘The egg itself had in each of these 
cases a cone, and near each spermatozo6n a minute aster. ‘The 
spermatozoén shown in Figure 17a was about 70 y distant from the 
egg nucleus (Fig. 17b), while the two supernumerary spermatozoa 
were each over 100 » distant from it. The relative nearness of the 
sperm figured, the large size of the aster, and especially the modified 
condition of the cytoplasm between the spermatozoén and the cone, 
make it appear probable that this is the one which would have 
been efficient in fertilization. 
In polyspermic eggs it is not always the case that only one sperma- 
tozodn becomes a nucleus. In Figures 19a, 19b and 19c are shown 
three nuclei which occur in one egg. Figure 19a, the largest one, 
represents the egg nucleus with its chromatin evenly distributed in a 
reticulum, and with no evidence of concentration of the cytoplasm 
or of astral figures in its vicinity. Figures 19b and 19c are two sperm 
nuclei of about equal size, each of about one-half the diameter of the 
egg nucleus, and very close to the surface of the egg; the chromatin 
in each case being evenly distributed, as in the egg nucleus. As 
shown in Figure 19b, a cone marks the end of the egg radius in which 
lies one of the sperm nuclei; in Figure 19c the nucleus has left traces 
of a “‘track”’ in the cytoplasm. In neither case was there any aster or 
centrosome apparent. One other egg (Figs. 20a and 20b) shows a 
condition, probably a later stage of polyspermy, in which there are 
two sperm nuclei. Both nuclei are in the same condition as the egg 
nucleus, and entirely separate from the latter and from each other, 
there being no contact where over-lapping is shown in Figure 20b. 
A definite funnel-shaped “track”? extends from the surface of the 
egg to this group of vesicles; indeed, a similar appearance is 
recognizable for a short distance beyond the deepest nucleus (Fig. 
20a). I believe the middle vesicle, which is slightly larger than either 
of the others, is the egg nucleus, and that each of the others is a sperm 
nucleus, one of which has approached the egg nucleus from either side. 
