592 GRIFFIN. [Vol. XV. 



improbable that two of the centers of radiation at the animal 

 pole are caused by and belong to the true centrosomes. 



In most cases the definitive asters appear on the side of the 

 nucleus nearest the egg surface, i.e., at the animal pole (PL 

 XXXI, Figs. 7, 8); but sometimes they appear laterally (PI. 

 XXXI, Fig. 9), as in Myzostoma, and they may occupy any 

 intermediate position. In such early stages I have never seen 

 both at the vegetative pole, though occasionally one may occupy 

 this position. From this it appears that the line joining the 

 centers of the asters (the future spindle-axis) may be inclined 

 to the egg-axis ^ at any angle from 0-90 degrees. 



Considerable variation also exists in the distance separating 

 the asters at their first appearance; for among eggs fixed at the 

 sa7nc period after fertilization and in ivliich the astei's have 

 attained the same degree of development, the angular distance 

 was found to measure from 45-90 degrees, or more. This pro- 

 duces a variation, not only in the length of the completed 

 spindle, but also in its position relative to the germinal vesicle. 

 In extreme cases, when the angle is very small, the main rays 

 may meet without penetrating the membrane, and thus results 

 a short spindle wholly without the nucleus and quite near the 

 surface of the egg. In this case it is the more lateral rays that 

 enter the nucleus and come into relation with the chromosomes. 

 The larger the angle, the longer and more centrally situated is 

 the spindle. When, as in most cases, the angle is great enough 

 to render the line joining the centrosomes secant to the nucleus, 

 then the median rays, which are destined by meeting equatori- 

 ally to form the spindle, push in the membrane and enter the 

 germinal vesicle. In this case the completed spindle is more 

 or less completely surrounded by the discarded chromatin-skein 

 (PI. XXXI, Fig. 10). This variation is of interest as bridging, 

 to some extent, the gap between such cases as the salamander 

 spermatocytes, where the amphiaster lies wholly without the 

 nucleus, and forms like Ophryotroclia {ovwcvi), Ascaris (spermato- 

 cytes), etc., where the nucleus comes to lie midway between the 

 asters (cf. Driiner, '95, and Braus, '95), and would seem to indi- 



1 By " egg-axis " is here meant the line joining the centers of the egg and of the 

 germinal vesicle. 



