ASSOCIATION OF CHROMOSOMES IN DIPTERA 245 



fiber. In the figure (169) the V-shaped chromosomes are all 

 seen edgewise, so that one arm lies almost directly below the 

 other (indicated by light shading.) The lower arms of the pair 

 on the left are not visible (apparently being cut off by the knife), 

 but the other two pairs are entire and clearly show the method 

 of division. It is perfectly plain that the two chromosomes in 

 the pair on the left have completely divided, that those in the 

 center have almost divided, while those on the right have only 

 partially divided and show the daughter halves attached for 

 some distance at their ends. Figure 171, in which only two of 

 the three pairs are drawn, shows the same features. It is ob- 

 vious that such figures as these could not possibly result from a 

 division in w^hich the two members of each pair went to oppo- 

 site poles, even supposing them to split in early anaphase as 

 conceived by Taylor and by Lomen. The figures reproduced 

 here are only a few from among many studied, all of which 

 present the same features. 



There can be no question, therefore, that in the ordinary 

 (diploid) mitoses in Culex, the two members of a chromosome 

 pair, lying side by side in the metaphase plate (figs. 166-168), 

 both split longitudinally in the equatorial plane (transversely 

 to the axis) of the spindle, and that each sends a V-shaped 

 daughter half to either pole, or in other words, that an equation 

 division is effected. This is in direct opposition to the ideas of 

 Taylor and of Lomen who concluded that the two members of 

 a pair lie one above the other in metaphase, that they go to 

 opposite poles in anaphase (effecting a reduction division) and 

 that as they go they split in a line parallel to the axis of the 

 spindle. As I have heretofore stated (p. 226) I believe that 

 Taylor's and Lomen's errors are due to poor preparations in 

 which the anaphase chromosomes were so massed together 

 as to entirely conceal their true nature and behavior. 



DISCUSSION 



One of the most interesting chapters in the history of modern 

 biological progress is that marked by the rise into prominence 

 of the 'chromosome theory' of heredity. And contributory 



