246 ULLIE. [Vol. XVII. 



and acts in a specific manner, it is best to designate it by a 

 special name. So I shall speak of it as the sphere substance, 

 following Conklin. 



During the growth of the sphere substance the two germ- 

 nuclei also have been enlarging. The individual chromosomes 

 do not form separate vesicles, as in so many eggs, but are 

 intimately united, apparently by processes sent out from the 

 chromosomes. The two germ-nuclei begin their growth at 

 the same time and keep pace with each other throughout the 

 process ; so that it would be impossible to distinguish them 

 apart were it not for their positions and the relation of the egg- 

 nucleus to the sphere substance. 



The migration of the two germ-nuclei begins simultaneously 

 some time before they have attained their full size. TJie egg- 

 nucleus is preceded in its first ■movements by the sphere substance, 

 which stretches out towards the side of the egg opposite to the 

 sper7n-nucleus (PL XXVI, Figs. 35 and 36); at the same time 

 the sphere substance undergoes a significant change of form, 

 elongating in an equatorial plane at right angles to the line 

 tmiting the two gertn-nuclei (PI. XXVI, Figs. 37 and 37 a). 



The egg-nucleus thus moves at first away from the sperm- 

 nucleus, which takes up its march in the direction of the former 

 (Figs. 35 and 36). So far as my observations go, this is invari- 

 ably the case. The two nuclei may meet a little to one side 

 of the center of the egg, in which case they soon move to 

 the center, or they may first come in contact at the center. 

 At the tim.e of their tneeting there is no itidication of an aster in 

 any part of the egg ; and I have only once found any such struc- 

 ture in the sphere substance ; in this case the aster was exceed- 

 ingly minute and no doubt sporadic in its appearance. In yet 

 another egg I found an amphiaster in connection with the egg 

 (.'') nucleus some time before the meeting of the two nuclei. 

 But this also was extremely unusual. 



To return to the sphere substance : I have already spoken of 

 its elongation in a horizontal plane at right angles to the line 

 uniting the two germ-nuclei (PI. XXVI, Fig. 37). This elonga- 

 tion continues until there is a relatively narrow bafid of sphere 

 substance stretching almost entirely across the egg (Fig. 37 a), at 



