no The Fly of Chirononms 



tubes, ovarian or seminal, enter paired ducts (oviducts 

 or vasa deferentia), which run lengthwise through the 

 abdomen. The ovarian or seminal tubes approximate to 

 the number of the segments, and sometimes give indica- 

 tions of segmental arrangement ^ ; they commonly enter 

 the ducts at right angles or nearly so, and from one side 

 only ^, 



In Ephemeridae ^ the outlets are double in both sexes, 

 and this we suppose to be the primitive arrangement. 

 In the great majority of insects, however, the ducts unite 

 behind ; and there may be a common tube, divided into 

 chambers of special functions, and receiving the secre- 

 tions of accessory glands. The common tube is usually 

 prolonged by the invagination, or inward telescoping, 

 of the integument around the outlet ; a considerable 

 section may thus be added to the original ducts, and 

 furnished with recesses, glands, &c., of its own. The 

 invaginated portion is usually lined by a chitinous 

 membrane, continuous with the chitinous cuticle of the 

 external surface^. The ovarian or seminal tubes often 

 deviate greatly from their original disposition. In the 

 male all, or all but one, of the seminal tubules may be 

 suppressed ; and the functional testis is then either 

 a dilatation of the sperm-duct, or a cajisule of similar 

 form. In the female the original number of ovarian 

 tubes is often retained, but they may be reduced or 

 greatly multiplied. In the earwig, for instance, there is 

 only one ovarian tube on each side, but this gives off 

 three longitudinal rows of short secondary tubes.'^ In 

 female Diptera we often hnd a similar arrangement, 



• .Tapyx, according to Grassi, AVi d. R. Ac. Lincei, 1888. 

 - Oudemans, 1887, pi. iii, figs. 41-43. 



•'■ Palmen, Puarige Ausfilhrungsgdnge d. GeschlecMsorgane bei Insecten (1884). 

 ' Palmen (loo. cit., pi. v) gives useful diagrams of the morphology of 

 the reproductive passages in a number of insects. 



* Dufour, Ann. Sci. Nat, xiii. (1828), 



