hargitt: pennaria tiarella and tubularia crocea. 177 



additional reason for the conclusion that the aster, when present, 

 owes its origin to the Spermatozoon, 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 spermatozoon 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 spermatozoon. In front of the sperm is an aster with no 

 visible centrosome. Two 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 spermatozoon a minute aster. The 

 spermatozoon shown in Figure 17a was about 70 /« distant from the 

 egg nucleus (Fig. 17b), while the two supernumerary spermatozoa 

 were each over 100 ft 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 spermatozoon 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- 

 tozoon 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 tq 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. 



