" HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 59 



At Columbia University, New York, where I have spent last 

 winter, I have had the best opportunity of doing this ; and 

 I want here to express my most sincere thanks to Professor E. 

 B. Wilson for offering me a table in his laboratory, for his gen- 

 erous liberality in giving me free use of his valuable material, and 

 for the lively interest with which he has followed my work. 



In this paper I wish to give a preliminary account of my re- 

 sults on Nereis limbata Ehlers, a species in which the chromo- 

 somes are especially favorable for an investigation of the mitotic 

 process — results which have obliged me to maintain a position 

 different from that represented in the papers of Gregoire and 

 Schreiner. 



The most important of these papers, it seems to me, is that of 

 A. and K. E. Schreiner on Tomopteris (1906a:). In this species 

 they have found an object, in which the whole maturation proc- 

 ess of the chromosomes can be followed and demonstrated 

 with an apparently indisputable clearness. After a comparison 

 of their results on Tomopteris with the maturation process in 

 other animals and plants (1906a and b), they find it very prob- 

 able that (p. 474., 1906^) " dieser Process bei alien hoheren or- 

 ganischen Wesen von einem gemeinsamen Gesetze geleitet wird, 

 das ihm unter ahnlichen Verhaltniszen ein ahnliches Geprage 

 aufdriickt, und zwar das Geprage des ' Tomopteris -Ty^us ' " ; 

 and also that (p. 475) " die Zeit nicht fern ist, wo das ' Reduk- 

 tionsproblem ' von morphologischem Gesichtspunkte aus als 

 gelost angesehen werden darf." 



I fully agree with A. and K. E. Schreiner, that the knowledge 

 of the maturation process in Tomopteris is of great importance for 

 our understanding of the same period in other organisms. 

 Especially valuable seems to me their convincing demonstration 

 of a parallel conjugation of the chromosomes in this species and 

 their identification of the same process in so many other 

 groups. 1 Of great value also are the demonstrations of Gregoire 



I I have reason to believe that the conjugation process in Enteroxenos follows the 

 type of Tomopteris more closely, than is shown in my figures (Bonnevie, 1906, fig. 

 33-42 and 159-162). During my first investigation of the spermatocytes of this 

 species I both observed and figured stages, in which there was a parallel arrangement 

 of thin chromatic threads, the ends of which were directed towards one pole of the 

 nucleus ; and it was, in fart, these pictures which made me join von Winiwarter 



