" HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 7 1 



visions, as well as from the later cleavage divisions, practically all 

 the chromosomes retaining their V- or horseshoe-shape and ac- 

 cordingly also their median point of attachment on the spindle (lat. 

 proph. of earl, cleav. div., p. 62). In the early anaphase we there- 

 fore here find a greater number of ring-shaped chromosomes than 

 in any of the other divisions. 



The aspect of the later anaphase seems at first to form a strik- 

 ing contrast to that of earlier stages, the daughter chromosomes 

 now being rodlike and terminally attached to the fibers. An 

 explanation is, however, found in the fact, that all these chromo- 

 somes show a more or less clearly visible longitudinal split, 

 which — as shown by the genesis of the chromosomes — is iden- 

 tical with the space between the two branches of a half ring. 



In several cases this split extends all through the daughter 

 chromosomes, so that they lose their V-shape, the two halves 

 being quite separate from each other (chrom. 34, p. 63). 



In the telophase the vacuoles are as a rule formed at the side of 

 such a double chromosome or between two neighboring ones. 



Later Cleavage Divisions. 

 (a) Seven and One Half to Eleven Hours After Fertilization. 



In the prophase of the later cleavage divisions we miss the 

 cross-shaped stage of the chromosomes. They appear within 

 the nucleus as longitudinally split ribbons (earl, proph., p. 62) ; 

 and at the time of attachment to the spindle fibers they are, 

 without exception, V- or horseshoe-shaped, being attached by 

 their middle point. 



The appearance of the later stages is, up to about nine hours 

 after fertilization, very much like that of the early cleavage, the 

 chromosomes retaining their prophase shape, until the daughter 

 chromosomes are separated. 



After this time, however, the aspect of the metaphase is changed 

 through a tendency in the two arms of the V-shaped chromosomes 

 to approach (chrom. 12 (26), earl, anaph., p. 6$).\ 



