204 KANSAS UNIVERSITY SCIENCE BULLETIN. 



move upon each other in such a way as to exactly reverse the 

 preexisting relation between the axes. How applicable this 

 observation may be to conditions in the Heraipteran cells, I do 

 not know ; but, judging from the great resemblance of the ele- 

 ments in the prophase, it would seem most reasonable to ex- 

 pect a similarity of the divisions. 



Paulmier (22) advances the suggestion that in the double-V 

 figures we may find a structure that will serve to reconcile the 

 divergent accounts concerning the longitudinal and cross divi- 

 sions of the tetrads. The only way in which this might be ac- 

 complished would be to suppose that each of the interspaces 

 represents a longitudinal cleavage of the thread, the first being 

 at right angles to the second. I have given this suggestion 

 careful consideration, and find no evidence to support it. The 

 double Vs are only of rare occurrence, the common element 

 being a straight rod, in the center of which is a diamond-shaped 

 clear spot representing the two planes of division laid out for 

 the spermatocyte mitoses. If two longitudinal divisions occur, 

 one must precede the other considerably and the resulting 

 halves become mutually repulsive, so that they move apart and 

 lie in one plane with only a slight connection at the point of 

 final separation. Moreover, the second cleavage must begin at 

 the opposite end of the segment and proceed in a reverse direc- 

 tion from the first. Not only this, but the first spermatocyte 

 mitosis divides the elements along what is generally conceded 

 to be the longitudinal split, and this must necessarily succeed 

 the supposititious first longitudinal cleavage by some time. 

 Without going into a consideration of these points, I may say 

 that they suggest such deviation from normal processes that 

 only extensive and acccurate observations would make Paul- 

 mier 's suggestion worthy of further consideration. 



(c) Formation of the Tetrads. 



In my former paper I reviewed the results obtained by Mont- 

 gomery upon the Hemiptera, but further notice of his work 

 will now be necessary, since on almost every important point 

 relating to chromosome structure he has changed his opinion. 

 His late extensive comparative study upon the Hemipteran 

 cells, as well as that upon Peripatus, will at the same time re- 

 ceive consideration. 



It appears from Montgomery's account that at the point 



