DEVELOPMENT OF THE OVARIKS TN THE BLOWFLY. 431 



Stein describes it as opening on the ventral surface in Beetles. 

 I formerly fell into the same error ; and it is exceedingly difficult 

 in dissections to determine this point. Sections of the entire 

 insect show at once the true relations of the parts. 



The pouch-like anterior part of the vagina is very distinct from 

 the posterior part ; that portion of it in front of the orifice of 

 the common oviduct (fig. 3, h) in the young insect is the lursa 

 copulatrix of authors. The hursa in the egg-laying insect is no 

 longer distinct, but forms the anterior part of the vaginal pouch. 



I shall call the vaginal pouch the uterus, a term applied to it 

 by Palmen (21) to distinguish it from the posterior tubular part 

 of the vagina. If the term is not morphologically, it is at least 

 physiologically correct, as an egg is frequently retained in it 

 until the embryo is ready to escape from the shell. 



There is at present some uncertainty as to the exact manner in 

 which the common oviduct is developed ; although it is quite 

 certain that the ovarian ducts are developed from the posterior 

 portion of the ovary, as Palmen has distinctly shown (21). The 

 same observer also shows that the vagina, uterus, and their appen- 

 dages are formed by an invagination of the external integument, 

 or rather of the hypoderm. My own observations entirely con- 

 firm Palmen' s statements. Although I have not been able to 

 trace the development of the common oviduct, its structure and 

 the manner in which the common duct of the testicles is formed 

 in the Fly (Weismann, I. c. Taf. xiv, fig. 68) indicate that it is 

 formed from the prolonged posterior parts of the ovaries. 



So far I have stated nothing concerning the anatomy of 

 these parts which has not been frequently observed and generally 

 admitted. I must now, however, enter into some details which 

 are not, so far as I know, to be found elsewhere. 



The common oviduct in the Blowfly terminates in two distinct 

 enlargements (figs. 1 and 3). The more anterior is due to a 

 thickening of its muscular coat where a thick retractor muscle 

 {m) is inserted into it. This witndraws the parts with the ovi- 

 positor. The second or terminal enlargement (os) is, however, a 

 pouch or bulb lined by a greatly plicated intima, and capable of 

 distention, so that it encloses the entire egg during its passage 

 through the oviduct. One egg is frequently found in this section 

 of the oviduct whilst another occupies the uterine cavity. 



