700 CLARENCE L. TURNER 
After the last division the chromatin collects at one side of the 
nucleus. There is a gradual reduction in size accompanied by a 
denser accumulation of chromatin at one side of the nucleus 
(fig. 42). The nucleus stains more darkly with each stage of 
progress toward the mature spermatozoon. 
7. Spermatozoa 
The mature spermatozoon has a blunt, kidney-shaped head 
which stains an intense black with iron-haematoxylin, a small, 
lightly staining middle piece and a short tail (fig. 43). The sper- 
matids of a single cyst, while transforming into spermatozoa, 
collect into masses which resemble parachutes (fig. 44). The 
heads all point in the same direction while the tails are drawn 
together. As the mature spermatozoa are formed the para- 
chutes become more compact, and in fixed material they may 
be teased apart without losing their shape. ‘These structures 
are probably comparable to the spermatophores described in 
some fishes. 
The first spermatozoa are formed about September 10th and 
are present until their expulsion takes place the following spring. 
The expulsion is not complete and a few scattered spermatozoa 
are still to be found in the testis during the early summer months, 
V. DISCUSSION OF FACTORS INFLUENCING CYCLE 
The three critical points in the variation of the testis, volu- 
metrically, are indicated in figure 1A. The first occurs in the 
latter part of August when the sudden increase in the size of 
the testis is started. The second is the beginning of the reduc- 
tion in size which occurs about November 1, and the third 
occurs about the middle of March when the volume suddenly 
begins to drop. 
In figure 4 an attempt is made to correlate the internal proc- 
esses with the curve in figure 14. Undoubtedly the tremendous 
increase in the volume of the testis is contemporaneous with the 
formation of the spermatogonia and the rapid subsequent divi- 
sions. While the maturation divisions are taking place new 
