4 STUDIES IN SPERMATOGENESIS. 



abundance of spindle fibers and sphere substance which were stained by 

 haematoxylin . The safranin -gentian combination used by Miss Wal- 

 lace and others in the study of the accessory chromosome did not prove 

 to be especially helpful with these forms. Thionin was found to be a 

 very useful stain for distinguishing between the accessory chromosome 

 and an ordinary nucleolus. Lacht-griin was often used in combination 

 with safranin. 



RESULTS OF INVESTIGATIONS. 



Termopsis angusticollis. 



In the termite it was not found to be practicable to dissect out the 

 testes. The tip of the abdomen was therefore fixed and sectioned, 

 young males whose wings were just apparent being used. The cells 

 are all small, and could not be studied to advantage with less than 

 1500 magnification (Zeiss oil immersion 2 mm., oc. 12). 



In the spermatogonium there is a very large nucleolus (plate i, 

 fig. i), which in the iron-hsematoxylin preparations is very conspic- 

 uous, but does not stain like chromatin with thionin or other anilin 

 stains, nor does it behave like an accessory chromosome during the 

 maturation mitoses. Before each spermatogonial division it divides 

 as in figures 2 and 3, and the same is true for each maturation mitosis. 

 Figure 4 shows the 52 chromosomes of a spermatogonial division in 

 metaphase. Figures 5 and 6 are young spermatocytes, showing the 

 division of the nucleolus. Figures 8, 9, and 10 show a stage imme- 

 diately following that shown in figure 6 and evidently persisting for 

 some time. The spireme thread is very fine, stains deeply, and is 

 wound into a dense ball, often concealing one (fig. 10) or both nucleoli 

 (fig. 8). Figure n shows the next stage ; the bivalent chromosomes 

 are so disposed as to give the familar " bouquet stage," with the loops 

 directed away from the centrosome and sphere (c). Figures 12, 13, 

 and 14 show the later development of the same stage, the chromatin 

 loops becoming thicker by the concentration of the smaller granules 

 to form the larger ones seen in figure 14. The loops now straighten 

 out and extend in various directions across the nuclear space (figs. 15, 

 16, 17). In fig. 18 a a longitudinal split is seen in several chromo- 

 somes. Figures i8, 19, 20, and 21 show various stages in the con- 

 traction of these split bivalent chromosomes to form diamond-shaped 

 tetrads, each side of which is a univalent daughter chromosome. The 

 tetrads come into the spindle in this form (figs. 22, 23), and change to 

 the form shown in figure 24 during the metaphase (figs. 22, 26, 28). 

 Figures 25 and 27 show the 26 bivalent chromosomes, or tetrads, in 



