Fig. 466.—t, testis; v, vas deferens; g, seminal vesicle of Acheta campestris.—After Carus, from Gegenbaur.
Fig. 467.—Male sexual apparatus of a bark-beetle: sl, vas deferens; ho, testis; bl, seminal vesicle; dr, accessory gland; ag, ductus ejaculatorius.—After Graber.
The number of testicular tubes is small in most Hemiptera, but very great in the Cicadidæ, Orthoptera, Coleoptera, and many Hymenoptera. Although the testes are usually separated from each other, they are closely united in certain Orthoptera (Gryllotalpa, Ephippigera), Coleoptera (Galerucella), in many Lepidoptera, and in a number of Hymenoptera (Scolia, Pompilus, Crabro, and others).
The two testes of most Lepidoptera are so closely grown together or coalesced into a single body that one might regard them as a single testis. But in the different families there occur all grades, from the unpaired testes of most Lepidoptera to Hepialus with separate testes. Cholodkowsky therefore distinguishes four types:—
1. The embryonal or primitive type, with two testes, whose seminal follicles are entirely separate. (Brandt.) These testes are contained, as in all other Lepidoptera, in a well-developed thick chitinous membrane or scrotum, analogous to that of the higher vertebrates, which envelops each separate seminal follicle (Hepialus humuli).
2. The larval type, with two testes, whose four follicles are enclosed by a common scrotal membrane (Bombyx mori, Gastropacha quercifolia, Ichthyura anachoreta and anastomosis, Saturnia pyri, Aglia tau).
3. The pupal type (since it first occurs in the pupa state), with a single testis, which possesses an external median lace-like covering. (Adela, Lycæna.)
4. The imaginal type, with a single testis enveloped by a lace-like scrotum, within which the follicles are wound around the longitudinal axis of the testis. (Most Lepidoptera.)
In Nematois there are twenty seminal follicles, the number of ovarian tubes being the same. (Cholodkowsky.)