256 KANSAS UNIVERSITY SCIENCE BULLETIN. 



when I published my first cytological paper, in 1898, I am able 

 to interpret the somewhat obscure phenomena of maturation 

 in this species more accurately than I could then. So far as 

 essentials are concerned, however, I find nothing to change 

 from the accounts in the previous papers, and I shall, for that 

 reason, not go into any great detail in my descriptions. Since 

 other investigators, utilizing similar material, have published 

 accounts that differ from my own in some particulars, I shall, 

 upon these points, speak more extensively. For the sake of 

 completeness I purpose to consider the diff"erent generations of 

 cells and to mention the phenomena that each exhibits, par- 

 ticularly those relating to the accessory chromosome. 



SPERMATOGONIA. 



A determination of the changes experienced by the elements 

 of this generation of cells is very difficult on account of the 

 small size of the cells, the number of chromosomes, and the 

 tendency of the chromosomes to fuse together under the action 

 of the fixing agents. It may be stated with reasonable cer- 

 tainty, however, that the number of chromosomes is the typical 

 one of the family. Of these thirty-three elements the accessory 

 chromosome is by far the most prominent in all the stages of 

 mitosis. The insertion of its fiber is median, and the halves of 

 the dividing chromosome go to the poles of the spindle as U- 

 shaped loops. While the limbs of the U are generally parallel, 

 they are sometimes widely separated, thus forming a V-shaped 

 figure. Because of their length, these parts of the accessory 

 chromosome remain for some time with their ends in the re- 

 gion of the equatorial plate, but they are gradually withdrawn 

 into the general mass of chromatin at the ends of the spindle. 

 (Figs. 1, 2, 3, 4, plate XV.) 



The ordinary chromosomes show some little diversity in size, 

 but they do not present favorable conditions for the study of 

 chromosome structure and behavior. Because of their number, 

 and the restrictions placed upon them by the size of the cell, 

 they form an almost solid mass of chromatin in the equatorial 

 plate during the metaphase. Favorable preparations show, 

 however, that the individual elements are distinct and united 

 together only by linin threads. In most cells, on the contrary, 

 the fixation has caused the confluence of all the chromosomes 

 into a plate with occasional apertures such as I described in 

 my former paper ('99, p. 188). 



