60 KRISTINE BONNEVIE. 



(1905) and of Schreiner (1906a: and b) of the close resemblance 

 between the chromosomes of very different species during the first 

 maturation mitosis ; and certainly, the presence of this same type 

 throughout the whole animal (and plant) kingdoms cannot but 

 give one the impression that (Schreiner, loc. cit.) " dieser Process 

 bei alien hoheren organischen Wesen von einem gemeinsamen 

 Gesetze geleitet wird." 



But what is the law that determines the behavior of the chro- 

 mosomes during the maturation period ? 



In my opinion the answer to this question is not yet given, in 

 spite of the apparently overwhelming evidence brought together 

 in the works of Gregoire and Schreiner to demonstrate that the 

 first maturation division is always a heterotypical one, and that 

 this heterotypical character finds its explanation in the fact, that 

 (Schreiner, 1906^, p. 44) " hier Ganzchromosomen, die nie 

 mit einander eine Einheitlichkeit gebildet haben, von einander 

 getrennt werden." 



My results in Nereis will, however, clearly demonstrate that a 

 " heterotypical " mitosis cannot be considered as identical with a 

 reductional one ; and I hope to show in the following pages that 

 the problem of the reduction of the chromosomes is still entirely 

 open to discussion. 



My material consisted of a most valuable series of maturation 

 and segmentation stages of Nereis limbata, collected by Professor 

 E. B. Wilson at Woods Hole, in 1 896-97. The sections as well as 

 the uncut material, fixed partly in picro-acetic acid, partly in 

 Flemming's fluid, proved to be still in perfectly good condition ; 

 and the material contains an uninterrupted series of stages, from 

 the moment of fertilization to the four-cell stage, and also the 

 later segmentation stages, up to fifteen and one half hours after 

 fertilization, these, however, with intervals in their development 

 of two to five hours. 



(1901) in his hypothesis of a parallel conjugation. As I, however, found very few 

 cells of the same appearance among the young oocytes, I did not believe this to be 

 the typical arrangement of the chromatin ; and I therefore tried to find other stages 

 showing the first traces of a parallelism between the thin threads. In the light of the 

 chromosome relations in Tomopheris I now think it probable, that a reinvestigation of 

 new material of Enteroxenos will give results somewhat different from those shown in 

 my paper. . (Added June, 1907.) This supposition is confirmed by Schreiner, 1907. 



