98 DR. C. L. BOULEXGER OX 



Mr. Crosslancl's collection are in what Wheeler (17) terms the 

 androgynous phase, both male and female oigans being fully 

 developed and functional *. The smaller specimens, however, 

 exhibit a marked protandiic condition ; as already mentioned, 

 those under about 1*5 mm. in length possess a well-developed 

 male apparatus of relatively greater size than in the adults. 

 Closer examination of such specimens reveals that whilst ripe 

 spermatozoa are present in abundance, the female organs are but 

 poorly developed, and mature ova absent or rare in the uterus 

 and oviduct. 



Male Organs. 



The testes, as in other Myzostomids, are much branched ; the 

 ramifications of each organ are for the most part restricted to 

 the ventral parenchyma below the alimentary canal, but occasional 

 dorsally directed branches are given off between the intestinal 

 and uterine diverticula. There is a single vas deferens on each 

 side of the body, which widens out distally to form a vesicula 

 seminalis, usually packed full of I'ipe spermatozoa, at the base of 

 the genital papilla. A short ductus ejaculatorius lined with 

 ectoderm leads through the papilla to the exterior. 



Female Organs. 



M. costaUir)i possesses a single pair of ovaries situated near the 

 middle of the body, ventro-laterally to the stomach, and occupying 

 the spaces between the four main intestinal trunks (text-iigs. 19, 

 21 A). In structure the ovaries resemble those of M. glabrum as 

 described by Wheeler (17), being irregular in shape; as a matter 

 of fact they are to be considered as formed by the proliferation 

 of the peritoneal epithelium at the terminations of ventrally 

 directed diverticula of a small ccelomic space, which occupies a 

 transverse position dorsal to the stomach in this region. The 

 uteriTS, as in other species, consists of a series of ramifying 

 cnelomic diverticula lying dorsal to the intestine and correspond- 

 ing roughly, both in number and arrangement, with tlie main 

 branches of this organ. The uteiine branches, like those of the 

 intestine, radiate outwards from near the centre of the body, 

 and arise fi'om the lateral terminations of the transverse coelomic 

 space mentioned above (text-fig. 22). This space and its ven- 

 trally directed diverticula which connect it with the ovaries are 

 lined by a low epithelium of small ciliated cells ; in the uterine 

 branches, which in adult specimens are filled witli ova in various 

 stages of development, this epithelial lining is absent, being 

 replaced by a " pseudoepithelium " similar to that desci-ibed by 

 von Stummer-Traunfels in AI. asterke (16). 



The oviduct is sharply marked off from the uterus ; it lies dorsal 

 to the stomach and rectum in the middle line, and has the form 

 of a straight wide tube, narrowing somewhat posteriorly, and 



* Cf. also Coventry (6). 



