78 KRISTINE BONNEVIE. 



(c) The conjugating chromosomes do not separate again ; but 

 their fusion may proceed so slowly that the appearance of the 

 following divisions is influenced by the doubleness of the chromo- 

 somes (Bonnevie, 1905, '06). 



Of these three possibilities only the first one will be treated 

 fully in this paper. 



According to the concordant results of modern investigators 

 the two longitudinally split halves of the chromosomes in the 

 prophase of the first maturation mitosis (a — a, p. 62) are to be 

 considered as two conjugating chromosomes united to form a 

 bivalent one. 1 



If, therefore, these two halves were separated from each other 

 in the first maturation division, then this division must with great 

 probability be considered as a reductional one, and all the sim- 

 ilar structures in the following divisions would have to be ex- 

 plained in some other way. 



Such a conclusion might, in Nereis, as in so many other ob- 

 jects, easily be drawn, if the chromosomes of the early prophase 

 are compared with those of the early anaphase ; it would, in- 

 deed, seem very natural to consider the thickening in the equator 

 of metaphase (or anaphase) chromosomes as identical with that 

 connecting their two halves in the early prophase. But be- 

 tween these two stages there is another, the stage in which the 

 chromosomes are first attached on the young spindle, 2 showing 

 that the long axes of the chromosomes are placed at right angles 

 to the axis of the spindle, that they are attached to the fibers at 

 the connection point between their two halves and divided in a 

 plane represented by their longitudinal split, and finally, that 

 their position parallel to the spindle fibers is secondary — reached 

 during the separation of their daughter chromosomes. 



If, therefore, the assumption is correct, that each half of the 

 chromosomes of the prophase represents -one of the conjugating 

 chromosomes, then the same must be true of the daughter chro- 



1 It makes here no difference, whether the conjugation of the chromosomes is con- 

 sidered as a parallel one or as having taken place "end to end "; in each case the 

 connection between the two conjugates is supposed to be of the same kind at a stage 

 directly preceding the maturation divisions. 



2 As will be shown in my final paper, there is no escape from this fact through the 

 suggestion that I should have " confondu les stades" (Gregoire, 1904, p. 307). 



