102 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
of the head (pi. 17, fig. 149); or else the head is considerably more con¬ 
tracted, with a single bend and a slight enlargement at the anterior 
end — the head piece formed by the centrosome. 
In figure 151 (pi. 17) is represented a group of ripe spermatocysts 
from a teased testis. In such fresh material one occasionally finds a 
mature spermatocyst discharging its spermatozoa (pi. 17, fig. 152). 
General Summary and Conclusions. 
1. Each testis originally resembles a simple gland with a duct and 
a terminal enlargement containing the germinal mass. 
2. The germinal mass is surrounded by a layer of cells resembling 
an epithelium, which early forms septa dividing the original follicle 
into four approximately equal follicles which, when the gonocysts are 
formed, differ considerably in size. These four follicles correspond 
to the four ovarian tubes of the female butterfly. 
3. The lining epithelium becomes early pigmented, giving the 
fully formed testis a bright red appearance. 
4. Outside the pigmented layer there is a thick tunica propria. 
As the right and left testes develop independently, they approach 
each other and become united in a double organ. 
5. The entire testis is surrounded by a thin tough tunica adventitia. 
6. The original germinal mass has the appearance of a syncytium 
out of which there is differentiated in each testis one or more large 
grandmother stem cells with protoplasmic processes connected with 
a mother branch cell. 
7. Surrounding the grandmother stem cell, its processes, and the 
mother branch cells, are nuclei probably derived from the original 
syncytium, the cortical nuclei. 
8. The primary spermatogonia are derived from the mother 
branch cells which divide regularly by mitosis, one half remaining 
attached to the grandmother cell and continuing thus to divide, the 
other half being separated and constituting the primary spermatogone. 
9. When a primary spermatogone is pinched off in mitosis, one or 
more of the cortical nuclei accompany it and furnish the “ anlagen” of 
the cyst cells. 
10. The grandmother stem cell does not divide by mitosis. 
11. There is at least one, but I have seen as many as four grand¬ 
mother stem cells in a testis. 
