432 PHYSIOLOGY OF THE INVERTEBRATA. 



posterior abdominal ganglion. The anterior end of the vas 

 deferens is dilated ; and this duct in the adult male always 

 contains spermatozoa. The spermatozoa appear to be formed 

 in the testis or mushroom-shaped gland of the young, and 

 then accumulate in the vas deferens, for in the adult cock- 

 roach the testis atrophies. 



The two ovaries, each of which consists of eight tubules, 

 are situated in the posterior part of the abdomen. The 

 ovarian tubes or the contracted portion of the ovaries pass 

 into two short oviducts. The two oviducts unite in the 

 middle line of the body, and open externally by a very short 

 but wide vagina. Behind the union of the oviducts with the 

 vagina, there is the spermatheca or seminal receptacle ; and 

 behind the latter are two much-branched tubular colleterial 

 glands which secrete the chitinous substance of the egg-cases. 

 There are siKteen eggs enclosed in each case. " The female 

 carries the egg-case about for a week or more, before 

 depositing it. The young leave the eggs as minute active 

 insects, colourless, except for the large dark eyes." Fzri- 

 planeta does not pass through any pupal stage ; but undergoes 

 seven ecdyses or moultings of the skin; and attains its 

 mature condition during the fifth year. 



The penes or male copulatory organs in the Insecta are 

 often very complex in structure. " Kraepelin,* who has 

 examined the development of these parts in the Drone, and 

 the modifications found in hermaphrodite Bees, is led .to the 

 conclusion that they are developed from the eighth and ninth 

 somites of the abdomen, and therefore are the homologues of 

 the parts of the sting in the female. In the male Blatta 

 (Periplaneta), however, it is obvious that the male copulatory 

 apparatus belongs to a more posterior somite than that upon 

 which the female gonapophyses are developed." 



In most Insecta, the vitellus of the ovum undergoes only 

 partial segmentation ; but in some Poduridce segmentation is 

 complete. During the development of the embryo, there are 

 * Zeitachrift filr Wiss. Zoologie, 1873. 



