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 IJtero-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 i mm. in length ; its muscular 

 wall is well developed, 'i mm. thick. Its cavity is ovoid, and 

 lined by a strong cuticular intima. It exhibits a pair of deep 

 pouches, the genital fossae, 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. 



