MUSEUM OF COMPARATIVE ZOOLOGY. 519 



is in this case a complete separation and subsequently a confluence of the 

 vegetative blastomere with one of the smaller cells at the animal pole. 



The equatorial zone of clear protoplasm occasionally seen in the eggs 

 of Limax (see p. 183) is possibly another phase of the protoplasmic activ- 

 ity which is usually manifest about the poles of the primitive axis. But 

 all these phenomena have been too little observed to afford grounds for 

 deciding on the nature of the forces which produce them. 



Asters. — Stellate figures make their appearance in connection with 

 two processes, — cell division, and the formation of the male pronucleus.* 



* The aster which accompanies the origin of the female pronucleus is one of the 

 asters of a cell division. It is possible that this aster is entitled to a separate desig- 

 nation, — female aster. The accounts given by Fol ('77'', pp. 450, 451) and 0. Hert- 

 wig ('78, p. 166) for the starfish are not in complete agreement. Fol says of the aster 

 which remains in the yolk after the elimination of the second polar globule, "II ne 

 tarde guere a s'effacer et a se changer en une ou deux petites taches," etc., and subse- 

 quently he says, " Les stries radiaires, peu accentuees du reste, que Ton remarque au- 

 tour du pronucleus en voie de croissance s'effacent et I'ovule entre maintenant dans 

 une nouvelle periode d'inactivite." Although he does not say definitely that there is 

 no connection between these two stars, I think it is fair to assume that to be his be- 

 lief, for he gives a figure of an intermediate stage (Fig. 12) in which no rays are rep- 

 resented. Hertwig, on the contrary, does not figure any stage in the early growth of 

 the female pronucleus which is destitute of rays. In the text he says that a quarter 

 of an hour after the fonnation of the second polar globule the homogeneous place ex- 

 isting in the egg, [the "area " of] the internal half of the amphiaster, has increased 

 in size and retired somewhat from the surface. A number of small vacuoles arise in 

 this homogeneous substance. In its vicinity the protoplasm toward the centre of the 

 egg has assumed a radial condition. The vacuoles increase in size, the radiation in 

 their vicinity becomes more distinct, and stretches out farther into neighboring parts. 

 During the confluence of the vacuoles, and the migration of the resulting Eikern 

 toward the centre of the yolk, the rays become less distinct and finally disappear. I 

 find in his account no ground for supposing that the rays about the female pronucleus 

 have an origin distinct from the deep aster. The nucleus, it is true, is represented by 

 both authors as occupying the centre of the radiation. That certainly is not the rela- 

 tion in ordinary cell division, and in so far a distinction is justified. The fact that this 

 radiation as described by Hertwig increases during the migration of the pronucleus and 

 then diminishes, also seems to warrant one in ascribing to it a significance difl"erent from 

 that prevailing in ordinary cell division. In Limax I find nothing to support Fol's view 

 of the separate origin of a female aster. The internal aster of the second archiamphi- 

 aster increases in extent toward the end of the formation of the second polar cell, and 

 possibly after its detachment also ; but whether this warrants a fundamental distinc- 

 tion from the asters of ordinary cell division seems very doubtful. There is little in 

 the conditions shown by Limax to support any argument drawn from the concentric 

 position of nucleus and aster (compare Figs. 57 - 60, 68, 72). Most of the investiga- 

 tions on other animals afford even less evidence than the starfish of the separate nature 



