William J. Moenkhaus 45 



long ones all grouped together on one side of the spindle (left in figure) 

 and the short ones on the other side. Whether all of each kind that 

 entered the resting nucleus have again appeared I cannot say, inasmuch 

 as it has been impossible thus far to recover all the chromosomes of each 

 parent. This is due to the complexity of the chromosome mass. The 

 chromosomes are so small and numerous that their number cannot be 

 determined even in the clearest preparation. In any given section some 

 of the long chromosomes are usually cut, making the pieces indistin- 

 guishable from the short ones, so that it is practically impossible to 

 follow out all of the chromosomes of each kind. That we have here to 

 do again, however, with the maternal and paternal chromosomes, there 

 cannot be the shadow of a doubt. 



Riickert, 95, in his Fig. 6, gives the lateral view of the anaphase of 

 the second cleavage spindles of Cyclops strenuous, both of which, but 

 especially the spindle to the right in the figure, sliow two groups of 

 chromosomes spatially separated in each half of the spindles. Kiickert 

 takes these to be the maternal and paternal groups of chromosomes, and 

 he gives, it would seem, very good reasons for thinking so. That the 

 two chromatin masses of the first cleavage represent the two parental 

 chromatins is beyond question. He is able to follow them from the time 

 of the conjugation of the two pronuclei through the various phases of 

 the division to the reconstruction of the resting nucleus. In this recon- 

 struction the first appearance of the nucleus is that of a double grou}) 

 of small vesicles. The vesicles of each group, it appears, fuse with each 

 other, the halves remaining distinct at first by the presence of a more or 

 less distinct wall and a corresponding constriction in the outer mem- 

 brane but later only by the latter. The two halves of the resting 

 nucleus, therefore, are to be identified as the maternal and paternal 

 portions. The emergence of two chromatin masses from this double 

 nucleus in the following division distributed on the spindle in the man- 

 ner above described, would strongly favor the view that the two sub- 

 stances had not mingled during the resting stage. Conversely, the 

 strong probability that the two chromatin masses remain distinct in the 

 previous resting nucleus argues strongly in favor of Riickert's supposi- 

 tion that the two groups of chromosomes appearing in the subsequent 

 division represent the maternal and paternal chromosomes. Conklin has 

 given very strong evidence for the same thing in Crepidula. It is appar- 

 ent to every one who has closely followed through the researches described 

 above that the one thing to be desired is better evidence that the 

 two groups of chromosomes emerging from the two bilobed resting nuclei 

 of the first two blastomeres are derived from the two lobes of the nuclei 



