250 BERTRAM G. SMITH. 



doubt in a number of cases, with no conflicting evidence. In the 

 anaphase each of the original chromosome groups has divided 

 equally (through the splitting of individual chromosomes), the 

 two halves going to different poles of the spindle. Each daughter- 

 nucleus thus receives two distinct groups of chromosomes, derived 

 from the egg-nucleus and the sperm-nucleus respectively. Al- 

 though in the anaphase and early telophase (Fig. 8) the paired 

 groups of chromosomes are not always very sharply separated, 

 yet there is no mingling of maternal and paternal chromosomes. 

 Finally, in the newly-formed daughter-nucleus each parental 

 group of chromosomes becomes metamorphosed into a separate 

 nuclear vesicle (Figs. 9 and 10). Except for a diminution in size, 

 which is afterwards partially made good by growth, each 

 daughter-nucleus closely simulates the original cleavage-nucleus 

 with its two resting germ-nuclei. 



The precise stage with newly-formed vesicular daughter-nuclei 

 has not been found in horizontal sections, hence all the figures of 

 this stage are taken from vertical sections (Figs. 9-12). During 

 the late phases of mitosis the two daughter-nuclei move some 

 distance apart; their path of separation is marked by a broad 

 trail of cytoplasm sharply defined from the surrounding yolk. 

 The division of the centrosphere or "attraction sphere" takes 

 place shortly before the daughter-nucleus assumes the vesicular 

 condition. The first cleavage furrow is not yet formed, but its 

 position, in a plane at right angles to the path of separation of 

 the two daughter-nuclei and midway between them, is visibly 

 indicated by a condensation of cytoplasm in the blastodisc. 



Aside from the fact that the two nuclear vesicles of a newly- 

 formed daughter-nucleus are always situated approximately equi- 

 distant from the plane of first cleavage, the orientation of these 

 nuclear vesicles with reference to each other is decidedly variable. 

 Since the two original germ-nuclei at the time of meeting usually 

 lie in the same horizontal plane (Figs. 2-4), we should expect the 

 same thing of the two vesicles of a daughter-nucleus; but in the 

 preparations studied these were more often found to lie in a plane 

 oblique to the horizontal, and sometimes one vesicle lies directly 

 above the other (Figs. 9 and 10). It should be remembered, 



