" HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 75 



takes place is given in the later cleavage divisions. The terminal 

 attachment of the tetrads in the metaphase is identical with the 

 median one of the V-shaped chromosomes in the prophase. The 

 tetrads are, however, as it were, pressed against the fibers of the 

 spindle, their proximal ends being thickened or curved (p. 62). 

 The point of attachment of the fibers is in this way changed from 

 a terminal into a subterminal one, the thickened ends of the 

 tetrads being found again as the short branch of the subterminally 

 attached daughter chromosomes. In some cases it seems as if 

 the point of attachment during the early anaphase is still further 

 removed from the end of the chromosome — a dislocation prob- 

 ably due to the fact, that the median part of the daughter chro- 

 mosomes makes less resistance against a separation than the ends. 

 (See the triangular chrom.; sec. mat. div., p. 63). 



3. What is the bearing of the chromosome-relations in Nereis 

 with regard to the assumption of a universally existing reduction 

 division ? 



In the papers of Schreiner (1904, 1906^ and b), Gregoire (1905) 

 and Montgomery (1905) the universality of a prereductional mode 

 of maturation is based upon the similarity between the chromo- 

 somes of different species, and more especially on the general 

 appearance of a " heterotypical " mitosis in the first maturation 

 division. 



Gregoire (1905) in his valuable review of the literature con- 

 cerning the maturation divisions in plants and animals, tries 

 to explain the phenomena in question as following his " heteroho- 

 meotypique " scheme — the first maturation division being a 

 heterotypical, the second a homeotypical one. 



His provisional definition of these two modes of mitosis and 

 his opinion with regard to their bearing is found in the following 

 sentences (Joe. cit., p. 254). 



" Pour la periode qui nous occupe, la caracteristique de l'het- 

 erotypie consiste dans la division longitudinale anaphasique ; la 

 caracteristique de l'homeotypie reside en ce que les chromosomes- 

 filles de cette cinese sont prepares des la cinese precedents par 

 une division longitudinale." 



" . . . ce schema, . . ., s'oppose directement au processus 

 postreductionnel, mais il laisse ouverte la question du processus 

 prereductionnel et du processus 'eumitotique." 



