80 KRISTINE BONNEVIE. 



sion also of a corresponding series of changes going on within 

 them during each mitosis. 



Whatever, therefore, the meaning may be of the different 

 structures of the chromosomes, they ought, I think, to be looked 

 upon from one and the same point of view in each of the matura- 

 tion divisions as in the cleavage, and the results reached in any 

 of these divisions may be used for an explanation of similar 

 structures in the others. 



According to this view, I consider the question of a reduction 

 division in Nereis as lying outside of the actual discussion until 

 a sufficient proof for its universality is established in other species. 



The questions to be settled with regard to Nereis concern the 

 two other possibilities, mentioned above — whether or not the 

 conjugating chromosomes have fused completely before the ma- 

 turation divisions. 



As I said before, I have not yet the material for a definite 

 answer of this question ; and it will be the aim of my following 

 investigations to procure such material through a comparative 

 study of the chromosomes of the germ track in Nereis and those 

 of other species. 



With our present knowledge of the chromosome-relations in 

 Nereis the evidences in favor of each of these views seem to 

 balance each other. 



If we take our starting point in the prophase of the first matur- 

 ation division, considering the two longitudinally split halves {a 

 and a, pp. 62-63) of the chromosomes as the conjugates being 

 terminally attached to the spindle, then it would seem natural to 

 look upon the quite similarly shaped chromosomes of the follow- 

 ing divisions from the same point of view. The gradual changes in 

 the whole appearance of the mitosis within the first 1 5 to 16 hours 

 after fertilization must then be considered as the expression of a 

 slowly proceeding fusion of the conjugating chromosomes (a and 

 a), their tendency of a divergence during the prophases gradually 

 decreasing, and their fusion during the anaphases becoming 

 always more complete. 



If on the other hand, we begin with the early cleavage divi- 

 sions, where all the chromosomes are V- or horseshoe-shaped 

 and with a median attachment to the fibers — then it would seem 



