74 KRISTINE BONNEVIE. 



somes in the early prophase. The prophase of the first matura- 

 tion mitosis is in most objects characterized by a more or less 

 complete separation of the longitudinal halves of the chromo- 

 somes — and in Nereis this separation may take place along both 

 longitudinal splits of the original tetrads. Also with regard to 

 this character we find a gradual return to the general type. 

 In the nuclei of the early blastomeres we still find a divergence 

 of the four arms of the tetrad, although here without the variety 

 in form characteristic of the first maturation division. Through 

 an approach of each two arms of the prophase-crosses, the V- 

 shaped chromosomes of the metaphase arise ; and in later cleav- 

 age-divisions the V-shaped chromosomes of the early prophase 

 are transformed into rod-like tetrads through a similar approach 

 of their arms. 



2. Another result of general interest, reached through a com- 

 parison of the maturation and cleavage divisions in Nereis, con- 

 cerns the point of attachment of the spindle fibers to the daughter 

 chromosomes. 



Although it seems, that the first connection between chromo- 

 somes and fibers always takes place at homologous points of the 

 chromosomes, there is a very strong evidence in favor of the 

 assumption that this point is changed during the mitosis. 1 



In the cleavage divisions all the chromosomes are derived from 

 the cross- or V-shaped chromosomes of the prophase, being 

 attached at their middle point. If, therefore, the point of attach- 

 ment is a fixed one, a subterminal attachment of the daughter 

 chromosomes would seem absolutely excluded. According to 

 the degree of opening of the longitudinal split the attachment of 

 the daughter chromosomes might be called a median or a ter- 

 minal one, but any intermediate attachment would seem impossi- 

 ble. And yet, we almost always find some of these chromosomes 

 subterminally attached — not so often in the early cleavage as in 

 the maturation and in the later cleavage divisions, where more 

 than half of the daughter chromosomes are often found to be sub- 

 terminally attached (see p. 63). 



An indication of the way in which this dislocation of the fibers 



1 This probability was, from another point of view first suggested by Schreiner, 1906^, 

 P- 433- 



