CHROMOSOMES AND SEX-DETERMINATION 405 



with iron haematoxylin, give very nearly the same series of 

 figures as are represented by Seiler. I have a few cases in 

 very early anaphase (just after metaphase) in which each 

 chromosome seems to be leaving behind, as its halves diverge 

 on the spindle, a mass of staining substance (cf. Seller's figs. 19- 

 22), and in later anaphase there is always an equatorial plate 

 of staining granules lying across the middle of the spindle. 

 Not infrequently these granules are elongated, so as to appear 

 like short threads, and some or all of them seem to lie on or 

 in the spindle fibres. Towards the end of the anaphase they 

 generally form a plate of fine-stained dots, of varying size, 

 and always more numerous than the chromosomes, as if 

 they had become broken up and scattered. During the 

 second division they sometimes become aggregated into a 

 sort of network (cf. Seiler 's fig. 35), or they may apparently 

 have become more finely divided and comparatively incon- 

 spicuous. 



Like Seiler, I find great variation among different polar 

 mitoses in respect of the amount of this eliminated substance. 

 In some spindles there is a dense equatorial mass, staining with 

 iron haematoxylin almost as deeply as the chromosomes 

 around the poles. In others the granules are much less con- 

 spicuous, in others again so few and small as hardly to be 

 noticeable. The amount of staining matter in the ' elimina- 

 tion plate ' varies in different eggs of the same female, and even 

 in eggs mounted on the same slide, though on the whole it is 

 more abundant in the eggs of some females than in those of 

 others. It is important to notice, however, that the apparent 

 amount varies with depth of staining, and when sections of 

 several eggs are mounted together on a slide it may happen 

 that some spindles are fully washed out, so that the chromo- 

 somes alone remain clearly stained, while a spindle in a neigh- 

 bouring egg may retain so much stain as to be useless for the 

 study of chromosomes. This variability probably arises from 

 differences of fixation due to variation in the penetrability of 

 the egg-shells to the fixative, and therefore it is not impossible 

 that the variation in the apparent amount of eliminated sub- 



