" HETEROTYPIC AL" MITOSIS IN NEREIS LI MB ATA. 65 



chromosome. The formation of rings seems, however, to be 

 limited to chromosomes of a certain size. 



At the time of the dissolution of the nuclear membrane the 

 chromosomes are found to be slightly contracted, and while some 

 of them regain their original tetrad-form, others remain like V- or 

 horseshoe-shaped rods, longitudinally split and with a thickening 

 at their middle point. Also the ring-shaped chfomosomes usu- 

 ally retain their form, while the numerous crosses, found within 

 the nucleus, are transformed into tetrads or V-shaped chromo- 

 somes. In only one case were two cross-shaped chromosomes 

 found attached to an early spindle. 



Considering the chromosomes of the prophase as different 

 modifications of the tetrad, we will find that their attachment to 

 the spindle-fibers is in all cases a terminal or a slightly subterminal 

 one. (See lat. proph. of 1st mat. div., p. 62). 



The unmodified tetrads are attached at one end, their longi- 

 tudinally split halves being separated from each other (chrom. 12, 



is)- 



The V- and horseshoe-shaped chromosomes are attached at 

 their middle point, this representing one end of the original tetrad 

 (chrom. 9, 10, 16). 



The rings are placed horizontally 1 on the spindle and the fibers 

 attached either at their transverse projections (chrom. 14) or at 

 the point opposite to these (chrom. 11). 



In each case the attachment is a terminal one, and the rings, 

 as also the V-shaped chromosomes, are divided along a plane 

 represented by their longitudinal split. In the above mentioned 

 case in which I have seen cross-shaped chromosomes attached to 

 the early spindle, the point of attachment seemed to be at their 

 center, all four arms being bent in a direction away from the axis 

 of the spindle (chrom. 17, p. 62). Considering the crosses as 

 tetrads with four diverging elements, we find here also a terminal 

 attachment of the fibers. 



Besides the forms already mentioned I also found, in two or 

 three cases, ring-shaped chromosomes placed in such a way on 

 the spindle that they must be divided into two half-rings (chrom. 

 13, p. 62). In all of these cases, however, the rings were smaller 



1 In the following description the axis of the spindle is always supposed to have 

 a vertical position. 



