298 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



drawings. Some chromosomes, such as 12 and 11 of series 2, 

 or 10 of series 19, show by the length of their transverse axis 

 that they have advanced farther in mitosis than many of their 

 neighbors. The chromosomes in column 9 seem all to belong 

 to the ring-like form. That in series 6 is not a ring now but it 

 may have been before it became drawn out so far. This is a 

 good example of a chromosome completely elongated in the 

 transverse direction. The No. 8's are all very constantly kid- 

 ney or bent-rod forms. There is very little difference in size 

 between them and the No. 7's. Of the No. 7's, nineteen out 

 of the twenty-five are rings. The others are usually of kidney 

 form. That in series 20 is rod-shaped. The point at which 

 the fibers attach is indicated by the X. In column 6 the chro- 

 mosomes are all kidney-shaped with two (series 23, 25), pos- 

 sibly one, exceptions. The exceptions may be considered ring 

 forms, but they may also be bent rods, for one of them (series 

 23) has the distal ends of the two halves of the ring not united 

 at all, while the other (6 of 25) is so nearly the size of chro- 

 mosome 4 of the same series, which is not a ring, that possibly 

 I may have the two interchanged. In column 5 is the acces- 

 sory. There is no trouble in finding the proper place for this 

 element, since it may always be recognized in the cell by its 

 form, and especially by its position in the cell-plate (figs. 30- 

 36.) In size it seems to fit between the No. 4's and 6's. On 

 account of its habit of starting off to the pole ahead of the 

 other chromosomes it so happens that it nearly always ap- 

 pears either in cross-section or a very much foreshortened side 

 view. Sometimes, but not often, it is seen in full lateral view 

 in the metaphase plate. As to individuality there is no mem- 

 ber of the complex that is more pronounced than the accessory. 

 It is the only element that may be traced from the prophases 

 of the spermatogonia through all the stages of the growth 

 period and the division stages of the first and second sper- 

 matocytes up to the spermatids. It seems at times to be an 

 element peculiar unto itself, and yet when viewed in the meta- 

 phases it behaves very much like the other chromosomes, even 

 so much so that it is with difficulty distinguished from some 

 of them (the 4's and 6's in first spermatocjrtes and- lO's in 

 spermatogonia). In all respects it is a chromosome, but one 

 whose individuality as to form, size, and habits is very strongly 

 marked. In column 4 about one-half the number are rings 



