INTERNAL GENERATIVE ORGANS OF THE FEMALE. 675 
unable to find the time to make more than a few cursory 
observations. I have examined numerous sections of these 
glands in Smerinthus populi, and their general structure is 
similar to those of the Blow-fly, but the cells are much smaller, 
and more columnar; the spherical corpuscles are also far 
smaller, and exhibit no zona radiata. I am, however, of 
opinion that they are similar in character, and their appear- 
ance, although less convincing than in the Blow-fly, is highly 
suggestive that they are concerned in the formation of germ 
ova. I shall return to this subject in a future section of this 
work. 
The Utero-vaginal Tube is the homologue of the ejaculatory 
duct and sac of the male. It is a thick-walled muscular tube, 
extending forwards from the vulva to the anterior edge of the 
fourth abdominal segment, when the long tubular ovipositor is 
retracted; but when the latter is exserted it is drawn out of 
the abdomen proper, and lies entirely in the interior of the 
ovipositor. 
Its anterior part, which is pyriform and has very thick 
walls, may be termed the uterus; the posterior part, which is 
cylindrical and has thinner walls, may be termed the vagina. 
The utero-vaginal tube is lined by a thick cuticular intima, 
which is separated from the muscular coat by a layer of pave- 
ment epithelium, resembling that of the cutaneous hypodermis. 
The Uterus, or bursa, clearly corresponds with the bursa 
copulatrix of the Lepidoptera and Homopterous Hemiptera. 
It measures rather more than 1 mm. in length; its muscular 
wall is well developed, ‘r mm. thick. Its cavity is ovoid, and 
lined by a strong cuticular intima. It exhibits a pair of deep 
pouches, the genital fosse, on its dorsal wall, which are 
separated by a well-marked ridge, the genital spine. The 
cuticular intima is very thick in this region, and exhibits a 
distinctly laminated structure. The ducts of the receptacula 
seminis open into the uterus immediately in front of the 
anterior extremity of the genital spine, close to the median line. 
The oviduct also opens into it on its dorsal wall, ‘I mm. in 
front of the anterior extremity of the genital spine. 
