vi INTERNAL STRUCTURE EGG 321 



The male sexual organs consist of the two testes placed in a 

 common capsule, from which proceed a pair of contiguous vasa 

 defereritia (dilated soon after their origin to form the vesiculae 

 seminales) ; into each vas there opens a long, tubular gland ; the 

 two vasa subsequently unite to form a long, coiled, ejaculatoiy 

 duct. It is in the structure of the female sexual organs that the 

 most remarkable of the anatomical characters of Lepidoptera is 

 found, there being two external sexual orifices. The imago has, 

 in the great majority of cases, four egg-tubes in each ovary ; the 

 pair of oviducts proceeding from them unite to form a single un- 

 paired (azygos) oviduct which terminates by an orifice quite at 

 the posterior extremity of the body. There is a sac, the bursa 

 copulatrix or copulatory pouch, which is prolonged in a tubular 

 manner, to open externally on the eighth ventral plate : a tube, 

 the seminal duct, connects the bursa with the oviduct, and on this 

 tube there may be a dilatation the sperrnatheca. Besides these 

 structures two sets of accessory glands open into the oviduct, an 

 unpaired gland, and a pair of glands. The development of these 

 structures has been described by Hatchett Jackson, 1 and exhibits 

 some very interesting features. The exact functions of the bursa 

 copulatrix and of the other structures are by no means clear. 

 According to Biley, 2 the spermatheca in Pronuba contains some 

 curious radiate bodies, and Godman and Salvin describe some- 

 thing of the same sort as existing in butterflies. Several varia- 

 tions in the details of the structure of these remarkably complex 

 passages have been described, and the various ducts are some- 

 times rendered more complex by diverticula attached to them. 

 Some noteworthy diversities in the main anatomical features 

 exist. According to Cholodkovsky, there is but one sexual 

 aperture the posterior one in Nematois metallicus ; while, 

 according to Brandt, the number of egg-tubes in a few cases 

 exceeds the normal four being in Sesia scoliaeformis fourteen. 

 In Nematois metallicus there is individual variation, the number 

 of tubes varying from twelve to twenty. 



The egg" has been more extensively studied in Lepidoptera. 

 than in any other Order of Insects. It displays great variety : 

 we meet with elongate forms (Fig. 164) and flat forms like 

 buttons, while in Linifn-oil,^ (Fig. 83, Vol. V.) the egg is a 



1 Tr. Linn. Soc. London (2), v. 1890, p. 143. 

 - P. ent. Soc. Washington, ii. 1892, p. 305. 

 VOL. VI Y 



