THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS PUPA. 87 



becomes tubular, tbe tube being formed from the oviduct, and forming eventually 

 the ventral portion of the bursal duct of the imago. 



(4) The posterior or oviducal aperture is at first close behind the anterior aper- 

 ture, but during pupal life shifts backwards and comes to be placed immediately 

 below or in front of the anus. 



(5) The bursa copulatrix and receptaculum seminis are both derived from a 

 paired anterior vesicle, invaginated from the hypodermis of the 8th somite in its 

 middle sternal region. The vesicle loses its paired character and overlies the 

 median section of the azygos oviduct. It grows in length antero-posteriorly. Its 

 anterior end becomes swollen and develops into the bursa copulatrix ; its posterior 

 end becomes elongated and pointed, and develops into the receptaculum seminis. 

 The rudiment of the bursa copulatrix gives origin to the terminal vesicular portion 

 of the organ and to that portion of the bursal duct which is dorsal to the point of 

 entrance to the seminal canal. The bursa and its duct at first open into the dorsal 

 aspect of the azygos oviduct ; they then shift to the left side and are continuous 

 with the tubular portion of the oviduct leading to the bursal aperture, which 

 becomes the portion of the bursal duct ventral to the point of entrance of the 

 seminal canal. Finally, the lateral connection between the bursal duct and the 

 azygos oviduct becomes tubular and forms the seminal canal. The rudiment of the 

 receptaculum seminis is at first bent down upon itself to the left side ; it increases 

 rapidly in length and straightens out. It has a transitory pyriform vesicle 

 appended to it. Later on it is differentiated into the three sections recognisable in 

 the imago. 



(6) The two sebaceous glands of the imago, their vesicles and common duct 

 leading to the azygos oviduct, are derived from the median dorsal portion of the 

 paired posterior vesicles invaginated from the hypodermis of the 9th sternal region, 

 whilst the common or basal ventral portion of the same vesicles becomes the 

 extreme posterior end of the azygos oviduct. The anterior end of the dorsal portion 

 retains an aperture into the azygos oviduct and becomes subsequently the tubular 

 duct and the vesicular dilatations of the glands. The posterior end of the dorsal 

 portion grows out into two tubes, a right and a left, the sebaceous glands proper. 

 They are at first curved upon themselves and parallel to one another. As they 

 lengthen they diverge and turn forward. 



(7) The odoriferous glands of Vanessa originate as separate tubular ingrowths, 

 a right and a left, from the hypodermis just in front of the oviducal aperture. 

 Later on they acquire a common vestibule. 



When the abdomen of the imago is completely developed within 

 the pupa, it is not only less in size and bulk, but also appears to 

 consist of only nine somites, of which the first is short, its sternum 

 fused to that of the second somite, its tergum composed of a middle 

 lobe and of two lateral lobes, its spiracle hidden at the bottom of a 

 deep recess. The following segments (2-7) with their spiracles are 

 quite distinct, but the 7th sternum is fused to the 8th abdominal 

 segment, which has a distinct tergum and sternum, the latter con- 

 taining the orifice of the bursa copulatrix. The spiracles of this (8th) 

 segment are lost, indeed, the atrophy of the tracheae which originates 

 from the abortive 8th spiracles of the pupa, is nearly complete by 

 the fourth or fifth day of pupal life in Vanessa io. Slight scars 

 indicating their position have been observed in a male pupa of Sphinx 

 ligustri. Beyond the 8th abdominal segment there remains the anal 

 cone or papilla which contains the oviducal aperture as well as the 

 anus, and is usually denominated the 9th somite. When the ovi- 

 ducal aperture shifts backward till it is close beneath the anus, an 

 ingrowth or fold of hypodermis takes place, surrounding the anus, the 

 oviducal aperture and the odoriferous glands. This fold corresponds 

 with a small portion only of the 10th somite, i.e., to the anal area. Con- 

 sequently it appears to be more correct to maintain, at least with 

 reference to Vanessa io, that the part of the abdomen from the posterior 

 edge of the 8th sternum and the spot where there is a slight fold 



