214 ZOOLOGY. 
are capable of being very deeply retracted, and as in 
Pentacta there are no tentacular ampulle. The small 
madreporic body is much as in Pentacta, and connects with 
a duct (madreporic canal) leading to the ring-canal. There 
are three Polian 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 fask-shaped, with the mouth and vent situ- 
ated near each other on the smaller end of the body. Th 
mouth is surrounded by ten tentacles, and there are ten 
papille 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 larvawhen 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. Itis 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 
