388 T^Taohide Yatsn. 



Immediately afterward the vegetative furrow cuts in at a rate two 

 or three times slower than that of the animal one. Sometimes the 

 vegetative furrow is very much reduced, and the constriction is 

 accomplished almost entirely by the animal furrow. ^'^ 



In sections of the eg}X of a late prophase we see precipitated 

 nuclear fluid around the spindle. At the metaphase this fluid takes 

 its definitive position around the equator of the spindle (''Biitschli's 

 space/' Khund)ler) (Text Fig. (\ l-.'5). As the chromosomes move 

 apart toward the poles, the nuclear fluid is taken into the spindle in 

 the form of dark granules. The spindle fibres too seem to absorb 

 the fluid into themselves, as shown by the fact that they are thicker 

 and stain darker in the middle. Spread over the animal half of the 

 egg is found a thin layer of cytoplasm rich in hyalo])lasm. This 

 layer is thickest in the middle and gradually thins out toward the 

 equator of the egg. This hyaloplasmic layer sends ofl" a vertical layer 

 to meet the nuclear stuff of Blitschli's space (Text Fig, D 1 and 2). 

 At later stages this hyaloplasmic cytoplasm is also found over the 

 vegetative pole. Thus the future cleavage plane is foreshadowed with 

 this plasm (''Diastem" His). Now this vertical septum begins to 

 become less dense. The cleavage furrows cut in along this thin hyalo- 

 plasmic cytoplasm. As the constriction proceeds a new ray system is 

 formed parallel to the spindle (sheaf rays) (Text Fig. C. 5). Dark 

 staining granules are laid down at the middle of both the sheaf rays 

 and spindle fibres. Later both kinds of fibres are bundled into a 

 sheaf. The chromatic granules fuse together and form a ring (mid- 

 body). 



(b) General Remarks. 



The methods which have hitherto been employed for the study of 

 cell-division mechanism may be classified under three categories, 

 namely, (a) observations on the normal processes of cell division 

 either in the living state or in fixed material, (b) the study of cell 

 division under modified conditions, (c) imitations of phenomena 



^*This mode of cleavage takes place, as I have often noticed, in artificial 

 parthenogenesis, since the egg nucleus usually lies near the animal pole (cf. 

 Morgan, '99, p. 452). 



