510 WARO NAKAHARA 
which is one of the commonest stoneflies in Ithaca (Smith, ’13), 
was then determined as best fitted for minute investigations, 
because of the favorable condition of its chromosomes. Since 
the spring of 1917 observation on this form has been carried on 
in the Laboratory of Histology and Embryology, Cornell Uni- 
versity, under the supervision of Prof. B. F. Kingsbury, whose 
helpful suggestions and criticisms given to me during the course 
of the work are most sincerely appreciated. A prolonged obser- 
vation was made with the greatest care I am capable of, and 
the numerous sketches made were carefully compared, and the 
working out of the history of the chromatin element was thus 
ventured. 
TECHNIQUE 
Flemming’s strong fluid has proved to be the best for fixing 
the testis dissected out in normal salt solution. Bouin’s picro- 
aceto-formol has also been used very frequently. Notwith- 
standing the powerful penetration of the fluid, the result was 
no better than that obtained from Flemming’s fluid. Bouin’s 
fluid tends to make the split line of the spireme more or less 
obscure, and the material of this fixation was thus found to be 
unfavorable for observations of certain critical stages. As far 
as the penetration is concerned, even Flemming’s fluid seems 
to be powerful enough, when applied on dissected material, 
to say nothing about Bouin’s. Addition of a small amount of 
urea to Bouin’s fluid (Hance, 717) did not make any noticeable 
change in the fixation from the original formula. 
Sections were cut from 7 to 10 uw thick and stained with Heiden- 
hain’s iron hematoxylin. The longer method with this stain, 
resulting in black coloring of the section, was more favorable 
than the shorter ‘blue’ method, especially for the observations 
on the nucleus in the early prophase of mitosis. 
DESCRIPTIVE 
Ten chromosomes appear in the spermatogonial division (figs. 
1 and 2). Looking at a metaphase plate from either pole, all 
of these ten can be individually recognized in every case. The 
