41)2 



TEXT-BOOK OF ENTOMOLOGY 



of insertion of the cords referred to becoming the openings of the vasa are car- 

 ried within the abdomen ; and this part of the integument becomes an unpaired 

 section. In these insects, also, there is an unpaired vesicula seminalis, but its 

 morphological nature (whether formed from the integumental duct or the fused 

 vasa deferentia) can only be settled after special investigation. 



In the Lepidoptera, also, it has been shown by Herold, Suckow, Bessels, and 

 recently with full details by Jackson, that the paired larval oviducts are at first 

 solid, but become tubular early in pupal life. A little later, their cavities open 

 into that of the azygos or unpaired oviduct. The paired oviducts open in the 

 female caterpillars on the hind edge of the 7th abdominal segment, afterwards 

 uniting with the unpaired vagina of the 8th segment, which is developed from 

 the hypodermis. 



Jackson adds that there are three stages traceable in the evolution of the 

 genital ducts of Lepidoptera: "an ephemeridal stage, which ends towards the 

 close of larval life ; an orthopteran stage, indicated during the quiescent period 

 preceding pupation ; and a lepidopteran stage, which begins with the com- 

 mencement of pupal life." 



As a summary of these results it appears that the genital organs 

 of insects consist of two morphologically different elements : 1. the 

 primitive internal paired structures (testes with the vasa deferentia; 



AS CD E F 



ovaries with the ovarian tubes), and 2. integumental structures 

 (Fig. 464). In the most primitive winged insects (Ephemeridae) the 

 latter structures are only represented by the two external sexual 

 openings, the entire reproductive system being paired. The paired 

 parts become in the more highly differentiated forms united into 

 single parts, while, a, a common integumental division, grows in, 

 forming the ductus ejaculatorius, or the vagina ; or, b, the inner pas- 

 sages anastomose together, i.e. the openings fuse together ; or, c, both 

 of these cases occur at once ; or, finally, we have d. where the super- 

 fluous paired parts by reduction become single. 



The male ducts open behind the 9th, the female passages of 

 Ephemerids behind the 7th abdominal segment, those of other 



