THE INTERNAL ANATOMY OF INSECTS 



161 



In the more common form, each testis is a compact body (Fig. 

 i8i, t) composed of a variable number of tubes corresponding with 

 the ovarian tubes, these are commonly called 

 the testicular follicles; but it would have been 

 better to have termed them the testicular tubes, 

 reserving the term follicle for their divisions. 



The testicular follicles vary in number, 

 form, and in their arrangement. In many 

 insects as the Neuroptera, the Hemiptera, the 

 Diptera, and in Campodea and Japyx, each 

 testis is composed of a single follicle. In some 

 beetles, Carabidse and Elateridae, the follicle 

 is long and rolled into a ball. In some Thy- 

 sanura the testicular follicles have a metameric 

 arrangement. 



In some Coleoptera, each testis is separated 

 into several masses, each having its own outlet 

 leading to the vas deferens; while in some 

 other insects the two testes approach each other 

 during the pupal stage and constitute in the 

 adult a single mass. 



The structure of a testicular follicle. — Like 

 the ovarian tubes, the testicular follicles are 

 lined with an epithelial layer, which is sup- 

 ported by a basement membrane, outside of 

 which there is a peritoneal envelope composed 

 And in these follicles a series of zones are 

 distinguished in which the genital cells are found in different stages 

 of development, corresponding to the successive generations of these 

 cells. In addition to the terminal filament four zones are recog- 

 nized as follows: 



The germarium. — This includes the primordial germ-cells and the 

 spermatogonia. 



The zone of growth. — Here are produced the spermatocytes of the 

 first order and the spermatocytes of the second order. 



The zone of division and reduction. — In this zone are produced the 

 Spermatids or immature spermatozoa. 



The zone of transformation. — Here the spermatids become sper- 

 matozoa. 



A discussion of the details of the development of the successive 

 generations of the genital cells of the male, or spermatogenesis, does 

 not fall within the scope of this volume. 



Fig. 1 8 1 . — D i agram of 

 the reproductive or- 

 gans of a male insect ; 

 the right testis is shown 

 in section; ag, acces- 

 sory glands; ed, eja- 

 culatory duct; ^i^, semi- 

 nal vesicles; t, testes; 

 vd, vasa deferentia. 



of connective tissue. 



