210 
Psyche 
[Aug.-Oct. 
becomes folded between the valves, as in Fig. 26. The endogy- 
nal plates eng shown in Fig. 26 are probably involved in the 
stretching of the membrane in question, though it apparently 
becomes distended and turgid by interal pressure also. At the 
base of the seventh sternite is the saccopore, or external opening 
of a ventral bilobed sac, the ventrosacculus sac , which apparent- 
ly serves as a glandular reservoir; and a repellent substance is se- 
creted in it. 
When the hypogyium or modified seventh abdominal sternite 
is removed, as in Fig. 19, the ovipositor or oviscapt with its basal 
plates etc., is exposed. As may be seen in Fig. 19, the eighth 
tergite is the dorsal portion of the eighth segment whose ventral 
parts form the structures labelled pvu etc. The sclerites pvu nor- 
mally project backward under the sclerites vs and conceal the 
latter, but in Fig. 19 the structures labelled pvu are represented 
as though forced back and upward in order to show the relation 
of the parts to one onother. Similarly, in Fig. 20 the sclerites 
pvu are represented as though laid back from the sclerite vs 
which they would normally cover and hide from view. The large 
cavity within the opening labelled vul in Fig. 20, is the uterus and 
vagina, or common passage of the two oviducts through which 
the eggs are conducted to the exterior from the ovaries where 
they are formed. The elongated opening of the vagina, labelled 
vul is the vulva, and the sclerites surrounding it are the perivulva 
pvu. Each half of the perivulva gives off an arm vbr, and the 
two halves are joined by an arch var. The walls of the vaginal 
cavity are membranous, and are thrown into folds in specimens 
treated with caustic potash. If this condition is normal, it would 
indicate that the vaginal cavity is capable of considerable dilation 
at the time of egg-laying, and the character of the perivaginal 1 
sclerites would indicate that the vulva might readily be widened 
considerably to permit the extrusion of a batch of eggs (the eggs j 
apparently are formed at about the same time) . If one observes j 
the relation of the sclerite pvu to the tergite of the eighth uromere 
in Fig. 19 (in which the plate in question has been forced back and 
the parts about it have been evertd) it would appear as though 
the perivulva pvu is a modified portion of the sternum of the 
eighth uromere. Paytoureau, 1895, however, and recent in- 
