CRITICISMS AND CONCLUSIONS. 59 



stages of the metaphase, and the latter two, having seen spindles in 

 oblique positions, apparently assume that Sobotta is right in his opinion 

 that the spindle becomes radial and that the oblique position is simply 

 an intermediate one. 



Division of First Spindle and Abstriction of First Polar Cell. 



Sobotta (1899) is the only observer who has figured stages in the 

 migration of the daughter chromosomes towards the poles of the spindle. 

 Because of the scarcity of such stages in his material he concludes that 

 the first spindle divides in only one-fifth of the eggs. In the other four- 

 fifths, therefore, the spindle does not divide and the first polar cell is 

 not cut off. This may possibly be due to a failure of the spindle to rotate 

 (Sobotta, 1907, p. 518, footnote). This he thinks agrees with his obser- 

 vation that 80 per cent of the fertilized eggs have only one polar cell, this 

 one being in his opinion the equivalent of the second polar cell of those 

 eggs which form two such cells. 



It has been shown (p. 16) that this stage is of very short duration. 

 Hence we draw the conclusion that the infrequent occurrence of this 

 stage is due, not to the failure of the spindle in some cases to divide, but 

 to the fact that the chances of meeting with it are few. 



Gerlach (1906, fig. 5) figures a recently formed polar cell in an ovarian 

 egg, but he says nothing about the division of the supposed first spindle 

 in oviducal eggs. As Sobotta points out, supposed first spindles in the 

 oviduct have had as much time in which to divide as have the first spin- 

 dles of adjacent eggs which have produced the first polar cells. These 

 considerations go to show that Gerlach misinterpreted the spindles in 

 oviducal eggs. 



In the opinion of Sobotta the "Zwischenkorperchen," sometimes 

 in two rows, are finally inclosed in the polar cell when it is cut off. He 

 describes and illustrates this condition in his papers of 1895 an( l !97- 

 Although his observations were really made on the second spindle, they 

 hold also for the first. It is difficult to account for this conclusion except 

 on the ground of variable conditions or poorly preserved material, for, 

 as Lams et Doorme (for the second spindle) and Gerlach show, and as 

 our material so clearly proves, the bodies in question do not lie inside 

 the membrane of either egg or polar cell. Gerlach, however, thinks they 

 are at first in two rows which then fuse. 



In the process of abstriction, as described on pp. 34 and 40, there 

 appears to be an attraction between the "Zwischenkorperchen" and 

 the vitelline membrane. Naturally any attraction between the mem- 

 brane and these bodies would be exerted more readily with the spindle 

 in an oblique or tangential position and its effect would be first manifested 

 on the side of the spindle nearest the surface. It is perhaps possible, 

 then, that the "Zwischenkorperchen" have some part to play in the 

 abstriction of the polar cell. 



