430 



PROF. B. T. LOWNE ON THE STRTJCTTJEE ATTD 



itself, it belongs entirely to the ovum, and cannot be regarded as 

 the epithelium of the ovarian follicle, wliich is quite distinct and 

 remains in the follicle. 



I am also inclined to regard the vitelline membrane as the 

 cuticular exudation from the inner surface of the epithelium of 

 the ovum and the chorion as the modified epithelium itself. The 

 cuticular sheath which leaves the ovarian follicle with the egg 

 is, I have little doubt, the epichorionic membrane described by 

 Leuckart, Eobin, and Kolliker. The shedding of the outermost 

 covering of the egg, probably the epichorionic membrane, and 

 possibly also of the epithelial chorion, was observed by Brandt 

 in the Tield-crickets in transit through the oviduct, forming 

 what he designates corpora lutea. 



The micropyle-canal, which, in the Diptera, extends the whole 

 length of the dorsal surface of the egg, is an infolding of the 

 chorion (PI. XXYIII. fig. 9). It is extended over the anterior 

 egg-pole (fig. 10), forming a considerable chamber in the floor 

 of which the micropyle is situated (fig. 10, m). 



The micropyle (figs. 12 & 13) is a small, almost quadrilateral 

 opening (fig. 12), 2'5 fx in diameter ; it is surrounded by a 

 number of radiating folds which project on the outer surface of 

 the chorion, and by a circular area composed of small hexagonal 

 cells. These correspond in size to the hexagonal fields with 

 which the rest of the chorion is sculptured. 



The open micropyle-canal is brought into relation first with 

 the orifices of the gum-glands, and later with those of the 

 spermatophorous capsules during the descent of the egg through 

 the genital canal. Henkiug (9) found spermatic filaments in the 

 micropyle-canal. 



3. The Oviducts and their Appendages. 



The general form and arrangement of these parts is well 

 known, so that the following description will suflice to indicate 

 their arrangement for my present purpose. 



The ovarian ducts are two in number (fig. 2), and these form 

 a common oviduct {od) by their union. The common oviduct 

 opens into the pouch-like anterior extremity of the vagina on its 

 dorsal aspect. 



