McCracken, Egg-laying Apparatus of Silkworm. 265 



communicates immediately (there being but a very minute inter- 

 vening canal) with the outside through a separate opening, the 

 copulatory pore (Fig. i, c). This is situated on the ventral sur- 

 face of the abdomen, ventrad of the ovipositor, in a recess betw^een 

 two chitinized plates, the one subtending the ovipositor, the other 

 ventrad of this one (Fig. I, V.pl.^ and F.pl.^). The opening is 

 controlled by sphincter muscles. The communicating tube 

 between the bursa and vagina is long (2^ mm.), narrow and direct. 

 The communicating tube between the spermatheca and vagina is 

 comparatively long, the spermathecal gland (Fig. i, Sp.gl.) open- 

 ing at the base of the spermatheca at its adjunct with the sperma- 

 thecal duct. 



At the time the adult leaves the cocoon, each ovariole or egg 

 chain contains from fifty to sixty fully formed eggs. (Dissection 

 of one abnormal individual showed six ovarioles upon each side 

 instead of the normal number of four.) 



In the functioning of the reproductive apparatus (primary and 

 accessory glands and ovipositing apparatus), therefore, the fol- 

 lowing must take place: 



(fl) The sperm is received into the bursa copulatrix and passes 

 through a considerable distance into the spermatheca. 



(b) From the spermatheca, surrounded by a fluid secreted by 

 the spermathecal gland, the sperm passes into the vagina. 



(c) Eggs pass down the ovarial tubes (ovarioles) enclosed by 

 a shell secreted by certain glandular cells in the ovarioles, and 

 reach the vagina. 



(d) Becoming fertilized and surrounded by fluid secreted by 

 the colleterial glands, the egg is passed on by the vagina to the 

 ovipositor. 



(^) Finally, the lips of the ovipositor open and each egg is 

 accurately placed by the side of another. In egg placing, the sen- 

 sory surface of the ovipositor is moved with dorso-ventral and 

 lateral movements, from right to left or left to right, avoiding each 

 previously placed egg. When the full quota of eggs have been 

 placed, they lie in several concentric rows, in a semi-circular area 

 (sometimes circular) about a center within which the moth has 

 been turning from side to side. 



The posterior abdominal ganglion (Fig. i, Ah.g.) is situated in 

 the fifth abdominal segment. The seven paired nerves of this 

 ganglion are distributed as follows: Nerves i and 2 to the mus- 



