132 ZOOLOGY. 



are capable of being very deeply retracted, and as in 

 Pentacta there are no tentacular ampullae. The small 

 madreporic body is much as^m Peniacta, and connects with 

 a duct (madreporic canal) leading to the ring-canal. There 

 are three Poliau vesicles, one fusiform and an inch in 

 length, the two others slenderer. The cloaca is of mod- 

 erate size, as in Pentacta, and the respiratory trees divide 

 at once into two very bushy branches. The ovarian tubes 

 form a brush or round broom-like mass or tuft, about an 

 inch long, the tubes small, yellow, and of nearly uniform 

 length, the oviduct straight and bound down to the walls 

 of the body. 



We might here mention the most aberrant type of Holo- 

 thurians, the Rhopalodina described by Semper, who states 

 that the body is flask-shaped, with the mouth and vent situ- 

 ated near each other on the smaller end of the body. The 

 mouth is surrounded by ten tentacles, and there are ten 

 papillae around the anus. There is a spacious cloaca or 

 respiratory tree. " Ten ambulacra diverge from the centre 

 of the enlarged aboral end of the body, and extend like so 

 many meridians to near the commencement of the neck of 

 the flask. In correspondence with each ambulacrum is a 

 longitudinal muscular band ; and it is an especial peculiarity 

 of Rhopalodina that five of these are attached to the anal 

 circlet, and five to the circum-cesophageal circlet" (Huxley). 

 The earlier stages of development of Holothurians, so far 

 as known, is like that of star-fishes. The larva when fully 

 grown is called an auricularia. It is transparent, cylindri- 

 cal, annulated, with four or five bands of cilia, and "usually 

 with certain ear- like projections, from which it derives the 

 name originally given to this larval form. Before the auri- 

 cularia is fully formed the young Holothurian begins to bud 

 out from near the side of the larval stomach, the calcareous, 

 cross-like spicules appear^ and the tentacles arise. The ear- 

 like projections disappear, the auricularia thus becoming 

 cylindrical. It is soon absorbed by the growing Holothurian, 

 which in some genera is strikingly worm-like, and it seems 

 that the Holothurian is more directly developed from the 

 larva than in the case of the star-fish and sea-urchins, the 



