86 BEITISH LEPIDOPTEEA. 



His results agree in the main with those of Herold, although certain 

 slight differences may be noted. It would appear that the two 

 filamentous oviducts are prolonged beyond their point of attach- 

 ment between the 7th and 8th somites as two separate broader 

 and longitudinally striated bands, which end in contact with two small 

 white knobs. They shorten gradually in the quiescent caterpillar, and 

 are thickened at the commencement of pupal life. By their union they 

 form the vagina. The two knobs just mentioned are, at the outset, 

 separated from one another by a slight space, and are fixed to the 

 hypodermis. A nerve derived from the terminal ganglion of the chain 

 passes to each of them. Whilst the formation of the vagina is taking 

 place, the knobs approach one another and unite ; moreover, they are 

 Drought, by the contraction of the muscles and skin in pupation, into 

 opposition with the attached ends of the two oviducts (a statement 

 which seems somewhat at variance with what is said as to the origin 

 of the vagina). They are destined to give rise to four swellings, the 

 rudiments of the bursa, the receptaculum, and the two sebaceous 

 glands. The latter, with a want of consistency, are said to be derived 

 from " the knobs themselves." 



Jackson's own investigations were carried out on Vanessa io, and 

 were particularly directed to the development of the azygos oviduct 

 with its accessory organs. He deals with five stages in the develop- 

 ment of the genital organs — (1) The full-grown caterpillar. (2) The 

 formation of the azygos oviduct, which occurs during the quiescent 

 period preceding pupation. (3) The stage during the time in which 

 the bursa copulatrix is still in direct union with the oviduct. (4) The 

 stage in which it acquires its adult indirect union. (5) The forma- 

 tion of the terminal papilla of the abdomen. 



It is totally impossible to discuss in detail the whole of Jackson's 

 observations showing in what points his conclusions differ from those 

 of Herold and Suckow, nor is this at all necessary as his paper is so 

 readily accessible. The following is a summary of the conclusions 

 arrived at on the subject {Trans. Linn. Soc. London, 2nd series, v., pp. 

 168 et seq.) : — 



(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 7th 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 hypodermic vesicle (5 infra). The 

 folds meet ventrally and fuse, leaving, however, an aperture, the future bursal aper- 

 ture. 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 subsequently becomes 

 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 rise 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 8th somite. At first it leads 

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



