THE SEA-URCHINS, SEA-CUCUMBERS, ETC, 
45 
of the eastern coast of the United States, Northern Europe, 
and the Arctic Seas. It is common among rocks, ranging 
from low-water mark to fifty or more fathoms. It eats sea- 
weeds, and is also a scaven- 
ger, feeding on dead fish, 
etc. We have observed great 
numbers of them assembled 
in large groups, feeding on 
fish offal, a few fathoms be- 
low the surface, in a harbor 
on the coast of Labrador, 
where fishing vessels were 
anchored. 
On placing an Echinus in 
sea-water the movements of 
the animal, especially its 
mode of drawing itself along 
by its numerous long tentacles, and how it covers itself by 
drawing together bits of sea-weed and gravel, may be ob- 
served. It has button-shaped organs of smell and taste. 
The shell consists of five double rows of limestone pieces 
called ambulacral plates, which are perforated for the exit 
of the tentacles or feet, which are like those of star-fish. 
There are also five double rows of inter amlidaoral plates, 
to which the spines are attached. The sand-cake urchin 
(Fig. 47) is very flat, with minute spines. 
Fig. 47 —Echinarachnius parma, com- 
mon Sand-cake. Natural size. 
Class IV. — Holothuroidea {Sea-cucumbers, Trepang), 
General Characters of Holothurians. — We now come to 
Echinoderms in which the body is usually long, cylindri- 
cal, with a tendency to become worm-like. The skin is 
not solid, and is muscular. Around the mouth are situated 
the ten branched gills, while the feet are arranged in five 
rows along the body. 
The trepang or beche-le-mer {HolotJiiiria edulis) is col- 
lected in the Moluccas and Australian seas, and when dried 
