CRUSTACEA— SEXUAL ORGANS 



375 



times are limited to the thorax, or to one portion of tlie thorax. In most Isopoda 

 the testis generally falls on each side into three pouches (Fig. 249, B), which, however, 

 possess a common vas deferens. The oviducts open in the antepeunltimate thoracic 

 segment into the brood cavity, receptacula seminis often developing at their ends. 



R 



V^^f^ 



Fig. 250.— Genital organs of Squilla mantis 

 (after Grobben). A, Stale, B, female organs, ct, 

 Posterior end of the cephalo - thoracic shield ; F7, 

 VII, Till, the 3 hindenuost free thoracic segments ; 

 t, testis ; vd, vas deferens ; d, appended glands ; ov, 

 ovary ; oi, oviduct ; rs, receptaculum seminis. 



Fio. 251.— Sexual organs of As- 

 tacus. A, female, B, male organs, ov, 

 Ovary ; u, unpaired portion of the 

 same ; od, oviduct ; oe, genital aper- 

 ture ; t, testes ; vd, vas deferens (after 

 Huxley). 



The female genital apertures very often (Isopoda, Anisopoda) only appear at the time 

 of the formation of the brood pouch. Peculiar phenomena appear at the time of 

 reproduction in the Oniscidce. The two receptacula (representing invaginations of 

 the outer integument) are at first not in open communication with the ends of the 

 oviducts. Only after sperm has, during copulation, entered the receptacula, do they 



