702 C. E. McCLUNG 



question of the position of fiber attachment, for, in case there 

 should be such an early separation of the chromatids in this plane, 

 the point of fiber attachment would still be at the synaptic ends, 

 whereas if there were a segregation division at this time it would 

 mean a shifting of the fiber attachment to the opposite ends. 



It is. not possible to come to a complete understanding of all 

 these changes and it may be that each of these conditions is met 

 in different forms. There are, however, a number of significant 

 facts which point to the interpretation I have advocated from 

 the first, i.e., of longitudinally split rods lying extended in 

 the equatorial plate with the median synaptic ends directed 

 toward the center of the plate and with fiber attachment at this 

 point. One of these is the case of the unequal tetrad discovered 

 by Wenrich in Phrynotettix, showing differential ends and divid- 

 ing so that each daughter cell receives equivalent parts. An- 

 other is an also unpublished series of circumstances in Trimero- 

 tropis, worked out by Miss Carothers, showing the attachment 

 of the so-called plasmasomes in such a way as to identify daughter 

 chromatids. Here also the parts are recognized according to 

 my description. The polar granules of Miss Pinney, the con- 

 stancy of fiber attachment in Stenobothrus, the occurrence of 

 cross-shaped chromosomes in the metaphase with one-half the 

 separation accomplished, and finally the appearance in Mecoste- 

 thus of a group of chromosomes, all but the smallest of which lie 

 extended in the equatorial plate, form a mass of evidence which 

 is most convincing when taken into consideration with that fur- 

 nished by other chromosomal forms. 



2. V-shaped tetrads. This form represents only a slight and 

 unimportant modification of the simple rod. It is, as has been 

 stated, such a chromosome bent at the synaptic point in the 

 plane of the longitudinal cleft with more or less separation of 

 the chromatids at the center. Such chromosomes appear in the 

 late prophase and are easily recognizable in the polar view of 

 the metaphase. They are shown in the figures of Sutton, Baum- 

 gartner, Davis, Nowlin, Granata, Payne and Robertson. 



An occasional and interesting prophase modification of the V 

 occurs when the chromatids separate along the longitudinal 



