168 PEOF. W. H. JACKSON ON THE 



(iii.) By a continuous longitudinal furrow crossing the eighth and ninth sternal 

 regions. 



(iv.) By a triangular forward extension of the sternal region of the ninth somite 

 invading the sternal region of the eighth, together with either (a) a linear 

 depression in the eighth sternal region, and another at the apex of the 

 triangular extension, or (b) a single depression close to or in the apex of the 

 triangular extension and produced by a confluence of the two depressions 

 before mentioned. 



§ 2. Development of the Azygos Oviduct and its accessory Organs in Vanessa Io. 



(1) The paired oviducts of the imago are developed from the larval oviducts. The 

 latter are, as stated by Herold, Suckow, and Bessels, attached at their ventral ends to 

 the hypodermis near the posterior margin of the seventh somite, close together and in 

 the median ventral line. They are at first solid, but acquire lumina early in pupal life. 

 A little later their lumina open into the lumen of the azygos oviduct. 



(2) The azygos oviduct is derived from the hypodermis ; it may be divided into three 

 sections, a median, an anterior, and a posterior. 



The median section develops as two folds, one on either side of the anterior hypo- 

 dermic vesicle (5 infra). The folds meet ventrally and fuse, leaving, however, an 

 aperture, the future bursal aperture. 



The anterior section, the first completed in order of time, appears to develop, so far as 

 its posterior portion is concerned, by the ventral union of two folds extending forwards 

 from the median section; but so far as its anterior portion is concerned as a solid 

 ingrowth of hypodermic cells which becomes subsequently tubular. The anterior end 

 of this section unites with the ventral ends of the larval oviducts while they are still 

 solid. 



The posterior section, the last to be completed in order of time, develops as a deep 

 furrow formed by two lateral folds, an extension backwards apparently of the lateral 

 folds, which give origin to the median section. They unite with the base of the posterior 

 hypodermic vesicles (6 infra). The future oviducal aperture is left when the base of the 

 posterior vesicle closes. 



(3) The anterior aperture of the azygos oviduct or bursal aperture retains a constant 

 position ; it opens in the sternal region of the eighth somite. At first it leads directly 

 into the azygos oviduct, but during growth the connection between the two becomes 

 tubular, the 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 aperture, 

 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 eighth somite in its middle 

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



