NEW MYZOSTOMA, PARASITIC IN A STARFISH. 77 



tached, on the dorsal surface of the stomach. It is in a very active stage 

 of proliferating the cell-triads (young oocytes with their attendant nurse- 

 cells). It is a single, unpaired organ of somewhat irregularly cruciform 

 outline when seen in the entire stained and cleared specimen. The body- 

 cavity which is developed only on the dorsal side of the gut-diverticula and 

 accompanies them in their ramifications, contains numerous ova (o.) in all 

 stages of growth, attached to the much flattened peritoneal epithelium. 

 The male reproductive organs present a very interesting structure and are 

 in different stages of development on the two sides of the body. On the 

 left side (right side of figure) these organs are highly developed and in 

 full activity, whereas on the left they are much atrophied. Each consists 

 of a penis (pn.) which has the form of a small conical papilla on the left, 

 but has all but disappeared on the right side, a ductus tjaciilatorius (d.e.} 

 which extends medially and divides into a shorter anterior and longer pos- 

 terior vas deferens (a.v.d. and/.2/.^). Each of the vasa defercntia again 

 divides into slender vasa efferentia (v.e.) which terminate in the testicular 

 follicles (/./.), well-developed and still containing mature spermatozoa on 

 the left side of the body, but exhausted and vestigial on the right. The 

 ducts and nearly all the follicles are situated on the ventral side of the gut- 

 diverticula. The specimen may be interpreted, in conformity with my 

 views on the sexual phases of Mysostoma, as about to pass from the func- 

 tional hermaphroditic to the purely female adult stage. 1 



The nephridia, " uterus" and cloaca resemble the corresponding struc- 

 tures in M. astcriie as figured by von Stummer-Traunfels (Taf. 34, figs. 

 4-9). The short, curved nephridia open on either side by means of dis- 

 tinct nephrostomes into the " uterus " (median body cavity) and by means 

 of their nephridiopores into the cloaca, there being no unpaired end-piece 

 as in some other species of Mysostoma. The cloaca is, however, much 

 shorter than in M. asterice. The "uterus" opens into it very near its 

 orifice on the dorsal surface of the body. The lateral organs also resemble 

 those of M. astericE in histological structure. The musculature of the 

 body and parapodia is very feebly developed, but the mesenchyma of the 

 former is abundant. The ventral nerve-ganglion lies in the middle of the 

 body beneath the stomach as in other myzostomes. It, too, is very small 

 compared with the nerve-ganglion of M. asteritz. 



1 These views on the protandric and hysterogynic nature of Myzostoma, advanced 

 in my papers entitled : " Protandric Hermaphroditism in Myzostoma," Zool. Anzeig., 

 No. 447, 17, Jahr. 9, pp. 178-182; and "The Sexual Phases of Myzostoma," Mitth. 

 Zool. Staz. Neapel., 17 Bd., 2 Heft, 1896, pp. 227-302, Taf. IO-I2 ; gave rise 

 some years ago to an unpleasant controversy with John Beard, who persisted in main- 

 taining the existence of complemental males among the Myzostomidse. It is a great 

 pleasure, after the lapse of a decade, to find that my views have been completely con- 

 firmed by so careful an investigator as von Stummer-Traunfels. In a forthcoming 

 paper on several new species of Myzostoma I shall produce still further proof of the 

 correctness of my contention. 



