142 THE VOYAGE OF H.M.S. CHALLENGER. 



simple or dichotomously branched cseca, attached one on each side of the medio- 

 dorsal mesentery. But in several representatives of the Elpidiidse, as, for instance, 

 Elpidia glacial is, Scotoplanes globosa, Scotoplanes robusta, Achlyonice paradoxa, &c, 

 there is only a single fascicle to be seen. As to their general appearance the generative 

 organs of this order present a great resemblance to those of the Dendrochirotse and the 

 Aspidochirotse, the former having two fascicles, the latter, with a few exceptions, but a 

 single one. 



Concerning the form, number, and size of the caeca which compose the reproductive 

 organs, there exists a great variation in the different species. The caeca of Oneirophanta 

 mutabilis are always unbranched, being more numerous, narrower, and more regularly 

 cylindrical in the males than in the females (PI. XLVI. figs. 6, 7). Deima fastosum 

 has the generative cseca, six to seven in each fascicle, unbranched and cylindrical, 

 (PI. XLVI. fig. 8), while the other species of the same genus has each fascicle made up 

 of five to six elongated very slender tubes, bearing larger and smaller spherical csecal 

 branches (PL XLVI. fig. 5). The reproductive organs in Eupkronides depressa are very 

 remarkable, for each fascicle — in the largest specimen, about 125 mm. long — is reduced 

 to a single tube, the posterior half of which is greatly distended so as to take the shape 

 of an oval elongated sac, covered with tuberculate protuberances (PI. XLVI. fig. 4). In 

 most cases, however, the reproductive organs of the Elasipoda are formed after the same 

 plan as those in other Holothurioidea, wherefore I refer to the description of the species 

 instead of detailing their shape here. 



But the genital glands of the different sexes do not always epiite agree with one 

 another, of which fact Benthodytes abyssicola, B. sordida, &c. (PI. XLVI. figs. 9 and 10), 

 afford striking examples, their male organs being composed of very numerous and 

 minute dichotomously branched cseca, while the female organs are very thin, and made 

 up of comparatively very few, large and voluminous, slightly dichotomous CEeca. 



The single efferent duct, attached to the medio-dorsal mesentery, passes forwards and 

 always opens in the medio-dorsal line, its communication with the exterior being commonly 

 at a rather considerable distance from the crown of tentacles. As a rule, the genital 

 aperture is situated immediately in the body-wall, but it is not infrequently placed at 

 the top of a genital process, which in Lcetmogone and Ilyodcenion attains a consider- 

 able length (PL XLIII. fig. 4, c, and PL XXXVIII. figs. 6, 7, 9). In one individual 

 of Lcetmogone ivyville-thomsoni I noticed that this genital process bore a small branch 

 near its middle, and in another specimen the top itself was divided into four parts. 



A transverse section of the genital process shows very distinctly that it is built up 

 of a very thick, dense, almost cartilaginous layer of connective tissue, the canal itself 

 being thus very narrow. At the base it may easily be observed that this layer is com- 

 posed of three different layers ; the outer, which is a continuation of the integument of the 

 body-wall itself, is separated from the inner, which has a yellow colour, by a dense 



