MOEPHOLOGT OF THE LEPIDOPTERA. 161 



(2) Formation of xIzygos Oviduct. 



The formation of the azygos oviduct, and the changes which accompany it, take 

 place during the quiescent period preceding pupation. The characteristics of this stage 

 may he summarized thus. They comprise : — 



(1) Changes in the two pairs of hyjiodermic vesicles of the larva ; 



(2) The formation of the azygos oviduct and the establishment of tlie apertures of 

 the bursa copulatrix as Avell as of the oviduct ; and 



(3) The connection of the paired larval oviducts to the azygos oviduct. 



It will be seen therefore that the second stage is one of prime importance in the 

 history of the organs with which this investigation deals. 



The first pair of vesicles loses completely all trace of its original paired character. 

 There is a gradual increase in size and at the same time an elongation in the antero- 

 posterior direction. The two ends of the vesicle increase in length and become pointed, 

 especially the posterior end (PL XVII. figs. 34, 37, be, rs.). And as the time of pupation 

 approaches, the anterior end becomes more swollen and even slightly bilobed, though 

 this, I am inclined to think, may be an abnormality, whilst the posterior end increases 

 still more in length, and is bent down upon itself to the left side (PI. XVII. fig. 36, 

 he, rs.). It is readily seen from a comparison with later stages tliat the swollen anterior 

 end of the vesicle is the future bursa copulatrix^ and the pointed posterior end the future 

 receptaculum seminis. 



The posterior pair of vesicles also increases in size and in length, and towards the end 

 of this stage gives origin to two posterior tubular processes (PI. XVIII. fig. 54>k, gl.). 

 The two processes increase in length and become curved ventrally upon themselves so 

 that they are cut twice over in sections taken from specimens about to pupate 

 (PI. XVIII. fig. 55 i, gl., gl.). In fact the external appearance at this stage is very similar 

 to what is seen in PI. XVII. figs. 38, 39, gl., gl. The dorsal median part of each vesicle is 

 converted partly into one of the tubular processes in question and partly into a common 

 or single short anterior portion, which subsequently connects the two tubes with what is 

 now the widely open basal portion of the vesicles from which the extreme posterior 

 portion of the azygos oviduct is developed, see figs, ^kg-b^^k, PI. XVIII. The basal or 

 oviducal portion closes ventrally, just before the larva becomes a pupa but remains in 

 continuity with the hypodermis. It leaves, wheu it closes, a small aperture, the future 

 oviducal aperture, at its anterior end (PL XVIII. figs. 55/", 55^). 



The azygos oviduct is formed in three portions : first, the part underlying the anterior 

 pair of vesicles, which is partly developed in the preceding stage ; secondly, the part 

 which connects the anterior vesicle to the larval oviducts, which is established next ; 

 and thirdly, the part connecting the anterior vesicle to the posterior vesicles. The two 

 latter parts differ in their mode of origin. 



The median portion is completed early in this stage. The two folds noted in th 

 previous stage, one on each side of the anterior vesicles (PL XVII. fig. 50, PL XVIII. 

 fig. 52, X , X ), increase in vertical height, and their lower margins approach and fuse. The 

 closure appears to take place first in front of the future bursal aperture and then behind it. 



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