HARGITT: PENNARIA TIARELLA and TUBULAR! a 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 spermatozoon. 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, 19c). 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 spermatozoon 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." The 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 



