476 BULLETIN OF THE 



(male pronucleus) was not observed in connection with this aster. From 

 among the large number of nuclear structures (nine in Lymna^us) that ap- 

 pear ill the yolk under the place of the polar globules in Biitschli's figures, 

 it is not possible to say always which represents the male pronucleus, 

 though there is usually one (Taf. IV. Figs. 7-9) which from its deeper 

 position or larger size may perhaps be inferred to be such. 



In Succinea the pronuclei closely resemble those which I have found 

 in Limax, the membrane (I) being much wrinkled by the action of acetic 

 acid. In Fig. 23 of Biitschli's Taf. IV. the nuclei occupy a peculiar po- 

 sition, their plane of contact lying in the animal radius of the yolk. I 

 have never seen just such a relation. Whether in Succinea the male 

 pronucleus is at any time surrounded with a radiate structure of the 

 yolk, does not appear from Biitschli's studies. I am inclined to think it 

 may be wanting, as in Limax. In view of the possible absence of stellate 

 figures in these cases, it still remains with me, as it was with Butschli, 

 an open question, whether the central stellate figure of his Fig. 4 is 

 really a newly formed aster. Against the probability of its having any- 

 thing to do with the male pronucleus, it may be urged, in addition to 

 the probable absence of a male aster, that no nuclear (vacuolar) structure 

 was observed in its immediate vicinity, and that the aster occupies the 

 centre of the yolk at so earli/ a stage. Butschli evidently inclines to the 

 opinion that it has no genetic connection with the first spindle. If he 

 is right, then it must be regarded as the male aster; but I am inclined 

 to believe, for the reasons just given, that it is the deeper star of the 

 second archiamphiaster, whose spindle has not been distinguished. 



Butschli endeavors (p. 391) to connect the "Neubildung" of nuclei 

 in the first segmentation sphere with the segregation of very clear nearly 

 homogeneous protoplasm. It is usually collected at the place where the 

 polar globules emerge, but it may be more widely distributed over the 

 surface, and may even (Nephelis) collect at a point within the yolk. 

 This clear protoplasm forms the centre of a system of rays, and within it 

 the new nuclei arise from very minute beginnings. These beginnings are 

 small compact corpuscles (p. 408) which rapidly become differentiated 

 into small vesicles. Just as in the formation of the nuclei in cell divis- 

 ion, so here the simplest primitive form is farthest from Auerbach's con- 

 ception, — an excavation in the protoplasm filled with a fluid, — it is a 

 homogeneous, compact condition. Since each of the several nuclei pos- 

 sesses the same histological structure as the nucleus which results from 

 their fusion, there is no ground for uniting with Selenka in calling the 

 former " nuclear germs,^' nor for saying, with Strasburger, that they are 



