ECHINODERMATA 251 
and the tube-feet. In Synapta ten auditory vesicles contain- 
ing numerous otoliths have been described at the base of the 
radial nerves. 
The generative organs are either a single gland situated at 
the left of the dorsal mesentery, or a double gland, one on each 
side of it; the glands are continuous with a single duct, which 
opens in the dorsal middle line close to the base of the ten- 
tacles. With one or two exceptions, the Holothuroidea are 
dioecious. 
The young of one species, Cucumaria crocea, found near 
the Falkland Isles, are attached in rows on each side of the 
dorsal ambulacrum. The early stages of developement ap- 
parently take place rapidly, and the embryos are arranged in 
position by the tube-feet of the ambulacrum. 
In the East Indies some species form an article of com- 
merce under the name of Béche-de-mer. They are dried and 
sold to the Chinese, who use them in the preparation of soup. 
The Holothuroidea are classified as follows : 
I. Actrnopopa.—Ladial canals present in the water-vascular 
system. 
a. Aspidochirotae—7he tentacles are peltate in form, 
respiratory trees are present. Holothuria, Miulleria. 
b. Elasipoda.— Tentacles as above. The dorsal tube-feet 
produced often into very long stiff processes.  Respira- 
tory trees rudimentary or absent. Stone canal sometimes 
opens to the exterior. Deima, Elpidia. 
ce. Dendrochirotae.— The tentacles have a dendriform shape. 
Cucumaria, Thyone. 
d. Molpadiidae.— The tentacles are simple or pinnate. The 
radial canals bear tentacles, but no other tube-feet. 
Molpadia, Caudina. 
II. Paractinopopa.— The tentacles are pinnate. No radial 
canals, no tube-feet, no respiratory trees. Synapta, Chirodota. 
