In many insects the testes are not composed of tubes (follicles), but of button-like bodies, each of which has its own duct.
The color of the testes is usually white, but they may be orange (Decticus), yellowish green (Locusta viridissima), or deep yellow (Chrysopa).
The testes of Asilid flies are enveloped by a common dark-red membrane rich in tracheæ, like that in Lepidoptera which clothes the separate testicular follicles. The two testes of Calliphora are enveloped by an orange-yellow capsule, outside of which is a special membrane formed by the fat-body. (Cholodkowsky.)
In the honey-bee the testis has two envelopes, the outer of which is formed by the fat-body, the inner coat of connective tissue. The entire testis corresponds to a portion only of that of Bombyx mori.
Fig. 468.—Male organs of a weevil, Hylobius abietis: H, testis; SL, vas deferens; D, slime gland; SB, seminal vesicle; uSG, ejaculatory duct.
Fig. 469.—Male organs of Tomicus. Lettering same as in Fig. 468.—This and Fig. 468 from Judeich and Nitsche.
The seminal ducts.—The vasa deferentia are fine tubes, which vary much in length; being short in many beetles and locusts, very short in many Diptera (Syrphidæ, etc.), very long in Cicada and many beetles; according to Burmeister, being in Dyticus about five times, in Necrophorus and Blaps eight to ten times, in Cicada 14 times, in Cetonia aurata 30 times, as long as the body. They either resemble a skein of silk, or form a tangled mass.
The distal or lower end of the vasa is in many insects dilated into a sac or seminal vesicle, which serves for the reception and storage of the seminal fluid after it passes through the vasa deferentia. In the honey-bee the vas deferens is given off from the reservoir, forms loops in and outside of the testis, and passes to the seminal vesicle. The canal into which the vesicle narrows does not open into the ductus ejaculatorius, but into the glandulæ mucosæ; its epithelial cells are much vacuolated, and have, therefore, a spongy appearance. (Koschewnikoff.)