312 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



The two stages immediately following the one shown in figure 

 9 must be studied side by side to interpret correctly the nature 

 of the changes which take place. In figure 10 the change 

 seems to be merely a closer aggregation of chromatin particles 

 in which a transverse striation is noticeable. Comparing this 

 with the following condition, seen in figure 11, we can plainly 

 see that the beginning of the prophase involves the organiza- 

 tion of the chromatin into a much convoluted thread.* 



The manner in which the condensed homogeneous elements 

 viewed in figure 1 are formed from the long, loosely organized 

 spirals of figure 13 is shown by a comparison of figures 10 to 15. 

 With the beginning of the prophase, figure 10, the contiguous 

 walls of certain vesicles disappear, resulting in a formation of 

 a few (actual number uncertain) large non-intercommunica- 

 ting vesicles each containing a number of rods showing a longi- 

 tudinal split. The accessory in figure 14 does not exhibit 

 this division. The entire disappearance of the chromosomal 

 vesicles and the arrangement of the chromosomes in the equa- 

 torial plate, figure 1, marks the completion of the series of 

 changes comprising one spermatogonial division. 



In the telophases of the last spermatogonial division the 

 changes are somewhat different from those just described. 

 The chromosomal vesicles, with the exception of that sur- 

 rounding the accessory chromosome, disappear with the dif- 

 fusion of the chromatin and the nucleus becomes spherical in 

 shape. The accessory seems to vary in the amount of diffu- 

 sion that it undergoes but is usually observed as a slender 

 black-staining rod closely appressed to the nuclear wall. 



FIRST SPERMATOCYTE. 



The diffused chromatin of the last spermatogonial telophase 

 is found in the early spermatocyte prophase to be reorganized 

 into a number of filiform segments which show a characteristic 

 arrangement. The accessory chromosome, a shapeless mass of 

 homogeneous chromatin, lies at one side of the cell (fig. 16 x). 

 Near it, and next to the nuclear wall, is a group of bodies 

 resembling the accessory in all but size, being much smaller. 

 From these the chromatic threads extend outward, each seg- 

 ment apparently forming a loop the ends of which have their 

 termination in the smaller chromatin bodies. A. and K. E. 



* The author was unacquainted with Bonnevie's worlJ, "Chromosomen Studien I, 

 Archiv fiir Zellforschung," Bd. 1, Ileft 2-3, which appeared after this was written, 

 and which describes similar changes. — C. E. M. 



