CRITICISMS AND CONCLUSIONS. 63 



statement of Sobotta, that there are fibers stretching from pole to pole, 

 and our own results. However, he gives the idea that such fibers form 

 a bundle on the outside of which the chromosomes rest and on which 

 they are drawn to the ends of the spindle, whereas the distribution of the 

 chromosomes in the plane of the equator in our preparations forces us 

 to conclude that such fibers, if present, must be interspersed among 

 the chromosomes. Sobotta (1895, p. 47) places the number at 12 (later 

 as probably 16). As it has not been possible to count them in our 

 preparations, we can not state what the number is. 



CENTROSOMES, CIRCUMPOLAR BODIES, AND CLEAR REGION. 



The circumpolar bodies and the clear region have already been con- 

 sidered. The former dwindle away in old second spindles, leaving what 

 might be mistaken for centrosomes (p. 39). Such remnants may well be 

 what Sobotta (1907) and Gerlach (1906) occasionaliy saw and what Lams 

 et Doorme (1907, figs. 6 to 8) and Kirkham (1907) found more regularly. 

 Lams et Doorme say that in the second spindle the " centrosomes" vary 

 according to the method of fixing. But in our opinion these are not to 

 be regarded as centrosomes. 



POSITION AND ORIENTATION. 



Gerlach (1906, pp. 18 to 20) and Kirkham (19076, p. 78) have 

 observed that the second spindle or second polar cell may be at various 

 distances from the first polar cell. Sobotta (1907, p. 532) finds only one 

 such condition in 1,000 eggs and thinks the difference between Gerlach's 

 material and his may be due to the fact that he and Gerlach used eggs 

 of different ovulations. We are at a loss to account for the difference 

 in Sobotta's material; but the fact nevertheless remains that the polar 

 cells may be found at various distances from each other. Gerlach 

 (1906, pp. 1 8 to 20) accounts for this by supposing the spindle to migrate 

 through the cytoplasm, and he figures a path which he thinks was made 

 by such a moving spindle. The distance, he believes, is determined by 

 the epoch of semination, because with that event the second spindle, 

 wherever it may be, stops in its migration and forms the second polar 

 cell (or at least divides) . There is no final proof that this migration does 

 not occur, but, from the evidence adduced (p. 43) in connection with 

 the position of the first polar cell, it seems simpler and more reasonable 

 to suppose that the polar cell shifts its position under the zona. This 

 shifting might be aided by the power the polar cell has of changing its 

 shape, as was observed by Tafani. Such an explanation makes it unnec- 

 essary to assume changes in the cytoplasm and a migration of the spindle 

 that is so out of harmony with what is known in other animals, where 

 the conditions are so favorable as to leave no doubt as to the events. 



The orientation of the second spindle is like that of the first and 

 needs no further discussion. 



