66 KRISTINE BONNEVIE. 



than those found within the nucleus, and which we have seen 

 placed horizontally on the spindle. I consider, therefore, that 

 this is undoubtedly a secondary ring formation, caused by a sub- 

 terminal attachment of the fibers to a tetrad-shaped chromosome. 1 



The early prophase, in which the chromosomes are yet quite 

 irregularly scattered on the surface of the spindle, is, according to 

 the above stated facts, characterized by an arrangement of the 

 chromosomes at right angles to the axis of the spindle. 



This stage is followed by another, in which this horizontal 

 position of the chromosomes is gradually changed into a vertical 

 one, the daughter chromosomes being pulled towards each pole 

 of the spindle (see earl, anaph. of 1st mat. div., p. 63). 



During the time in which this separation takes place the chro- 

 mosomes very often pass through a second cross-like stage 

 (chrom. 18, 19, 22), the fibers being attached at or near the 

 ends of the vertical arms of the cross. At first the horizontal 

 arms are relatively long ; a longitudinal split may be clearly 

 visible in them, and they are often bent (in a direction away from 



1 The behavior of the ring-shaped chromosomes in Nereis confirms my conclusion 

 from Enteroxenos (Bonnevie, 1905, 1906) that the rings of the prophase cannot always 

 be considered as identical with those of the metaphase. The prophase rings are 

 in Nereis divided in their own plane, and during the separation of the daughter- 

 chromosomes other rings are transiently formed from tetrads and V-shaped chromo- 

 somes ; these metaphase rings are then sooner or later divided into two half rings. 



According to a note in their latest work A. and K. E. Schreiner ( 1906^, p. 442) 

 seem to have observed metaphase-rings in the first maturation division of Enteroxenos. 

 This fact does, however, neither change nor contradict my results on the same spe- 

 cies, that other rings are divided in their own plane and thus still appear as rings in 

 the telophase. 



In the same paper (Schreiner, 1906^, p. 444), is found the following phrase : 



" Die Verfasser (Farmer u. Moore) meinen jetzt, wie Montgomery und Bonnevie, 

 dass die bivalenten Chromosomen nicht durch Spaltung der in reduzierter Zahl vor- 

 handenen Schlingen, sondern durch Zussammenbiegung derselben gebildet werden." 



Because of this misleading account I want here once more to state my exact posi- 

 tion with regard to these questions. I have described the bivalent chromosomes aris- 

 ing through a parallel conjugation of two homologous univalent ones — a view which 

 is very different from that held by Montgomery and by Farmer and Moore. And with 

 regard to ring-shaped chromosomes, I have shown that they may be formed in different 

 ways, through an approach of the free ends of a chromosome (postsynapsis of Enter- 

 oxenos"), or through a widening of a longitudinal split, while the two halves of the 

 chromosome are still connected at their ends (cleavage division of Enteroxenos and 

 many cases described in the literature). And further, that from the presence of ring- 

 shaped chromosomes no conclusions can be drawn with regard to the nature of the 

 mitosis, as it has been shown that rings may divide in two different planes. 



