270 PHYLUM ECHINODERMA. 
organs,” which emit white conical bodies from the cloaca 
when the animal is irritated. The bodies remain adherent 
by their bases, are greatly elongated by internal fluid 
pressure into sticky tubes which break off. They will 
adhere to almost everything but the Holothurian itself. 
Those Holothurians, e.g. Holothuria nigra, in which the 
organs are well developed are often called “cotton- 
spinners,” on account of the dense mass of viscid substance 
which they eject. A little fish, Averasfer, introduces itself 
—tail first—into the cloaca of several Holothurians, and 
lives three as an innocent commensal. 
The water-vascular system shows many peculiarities. In what, by 
analogy with the other classes, may be described as the primitive 
condition, there is « ring canal round the mouth communicating with 
the exterior by a stone canal, with one or more Polian vesicles hanging 
in the body cavity, and with five radial canals. The radial canals, as 
in starfishes and sea-urchins, are connected with internal ampullee and 
external tube-feet. The anterior tube-feet are greatly enlarged and 
modified to form the tentacles which encircle the mouth. It is, how- 
ever, only rarely that the water-vascular system exhibits this primitive 
condition. In most cases the stone canal loses its original connection 
with the exterior and opens merely into the body cavity ; often it is 
represented by numerous small canals, hanging freely in the body 
cavity (Fig. 139, s¢.). Certain of the tube-feet are always modified to 
form tentacles, and these may, as in Syzafta, be the only representatives 
of the tube-feet. In regard to the function and degree of development 
of these, there is indeed much variation. 
The blood-vascular system consists of a circum-cesophageal ring and 
vessels to the alimentary canal and the gonads. The system is in great 
part lacunar. There is also a pseud-hamal system. 
The sexes are usually separate. The reproductive organs 
do not exhibit radial symmetry, and are branched tubes 
which open within or just outside the circle of tentacles. 
Like other internal organs of Holothurians, they are often 
very brightly coloured. ‘The larva is, in most cases, what 
is known as an Awricularia. Sometimes, however, the 
larval stage is skipped, as in Cucumaria crocea and Psolus 
ephippifer, where the eggs and young are attached to the 
back of the mother. In C. cuvata the eggs and young are 
sheltered on the ventral surface; in C. parva in a shallow 
ventral insinking; in C. /evigata there is an invaginated 
ventral brood-pouch ; in Chiridota contorta the young are 
sheltered in the genital tubules; in Sywapta vivifara and 
