MUNSON: SPERMATOGENESIS OF PAPILIO. 
51 
As the two testes grow they gradually approach each other (pi. 12, 
fig. 6), and finally fuse into a spherical body, the right and left halves 
of which are indicated externally by a groove as shown in plate 12, 
figure 7, t. The two vasa deferentia also become intimately united 
at the point of insertion into the testis proper (pi. 12, figs. 5, 7). The 
two testes then become surrounded by a continuous, comparatively 
thick connective-tissue layer, the tunica propria (pi. 12, fig. 8, cn. 1.) 
which extends also down between the two halves, but does not dip 
down between the follicles. Outside the tunica propria, there is finally 
a thin epithelial investing membrane, tunica adventitia, which is also 
continued over the vas deferens (pi. 12, figs. 5, 8, pt. to.). 
The inner lining of the follicles early becomes richly pigmented, 
and this red pigment resisting to a remarkable degree the decolorizing 
effects of reagents, gives the whole organ a bright red appearance, 
which facilitates considerably this study, since the testes can easily 
be seen with the naked eye even in the unstained larva sectioned in 
toto. In teasing the testes the pigmented lining epithelium (pi. 12, 
fig. 8, p. 1.) and the tunica propria ( cn. 1.) rupture easily. But the 
outer tunica adventitia (fig. 8, pt. to.) is quite tough and elastic, allow¬ 
ing the spermatozoa and cysts to accumulate between it and the 
tunica propria. 
I have been unable to arrive at any definite conclusion as to how 
this union of the two testes, and their final inclusion within a continu¬ 
ous membrane is brought about. I assume that it results from the 
increase in size. As the two testes grow they encroach on the surround¬ 
ing connective tissue of the body which finally becomes compressed 
between them and crowded over the surface till it constitutes a com¬ 
paratively thick investing membrane. 
I find these relations of the testes to each other and to the surround¬ 
ing stroma to be the same in Grapta silenus (pi. 12, fig. 8 b). Here, 
as in Papilio rutulus, there are four follicles in each testis. In Grapta 
silenus, however, the inner pigmented layer is relatively more developed 
and the nuclei much more stainable and prominent, but the tunica 
propria is less developed (compare pi. 12, fig. 8 and fig. 8 b). 
Nomenclature. 
We are indebted to La Valette St. George for the terminology 
usually employed in this subject. I use this terminology so far as it 
suffices; but, as there are some facts brought to light in my work 
