" heterotypical" mitosis in nereis limbata. 77 



" Nach der Einstellung in die Teilungsebene zeigen die Chromo- 

 somen in gewissen Fallen die fur die I Reifungsmitose so char- 

 akteristischen, in die Aquatorialebene fallenden Verdikkungen 

 und seitlichen Auslaufer, die sicher beweisen, dass es die Spalt- 

 halften der bivalenten Schlingen, die Konjuganten, sind, die 

 hier getrennt werden." 



The above cited sentences of Gregoire and Schreiner contain 

 the view which forms the basis in their generalizations with regard 

 to the reduction division. 



Judging the chromosome relations in Nereis from the same 

 point of view, we should find a reduction of the chromosomes 

 taking place not only in each maturation division but also in each 

 of a whole series of cleavage divisions. The early separation of 

 the daughter chromosomes, the heterotypical shape of the chro- 

 mosomes in metaphase, and their doubleness in the anaphase, are 

 characters common to all these divisions. 



This result is so clear and its consequences are so evident, that 

 a further discussion upon this point would seem unnecessary. 

 Before the question about the nature of the maturation divisions 

 can be considered ripe for new generalizations, it will be neces- 

 sary to widen the base of our investigations to a comparative 

 study not only of the maturation process itself, but also of the 

 changes of the chromosomes during the time following this 

 period. 



Though, however, the main base of the modern generalizations 

 is removed through the knowledge of the chromosome relations 

 in Nereis, it is not therefore excluded, that a reduction division 

 may exist in this species as well as in others ; and we now finally 

 turn to the question : 



4. How is the maturation process in Nereis to be understood ? 



In answering this question three different possibilities must be 

 considered, all of which have already been applied for the ma- 

 turation process in other species. 



{a) One of the maturation divisions is a reductional one, sepa- 

 rating chromosomes, which have conjugated at an earlier period. 



(J?) Both maturation divisions are to be considered as ordinary 

 mitoses, the conjugating chromosomes having fused completely 

 with each other (Boveri, 1890). 



