52 
ROOM X. 
Nat. Hist. 
taining those which have a small orbicular body and 
long, subcylindrical arms, as the Medusa’s Heads (Eu- 
ryale), which have the arms very long, with com¬ 
plex ramifications, so as to end in an immense multi¬ 
tude of small threads. In most of the species the arms 
are branched at the base, but in one (Euryale palmi- 
fera), the base of the arms is simple, and the tip re¬ 
peatedly ramified. 
The Ophiurae have also very long and slender arms, 
but they are always simple. In many of the species the 
arms are furnished on each side with several series of 
minute, moveable spines. 
The arms of the true Star-Fish (Asterias) are a mere 
extension of the substance of the body, and of an uni¬ 
form structure with it. Most of the species have the 
faculty of reproducing the arms, or such parts of them 
as may be accidentally broken off; and if an entire arm 
be separated, provided a part of the body be attached 
to it, other arms are reproduced, and a perfect fresh 
animal is formed. Some specimens illustrative of these 
facts are in the Case No. 10. 
The Asterise differ greatly from one another both in 
texture and form. Most of the species have five rays, 
but varieties are sometimes met with which have only 
four rays, one of which is in Case No. 17. Some species 
have eight, others nine, and again others from twelve to 
thirty rays. 
The Sea-Eggs are at once known from the Star-Fish 
by their body not being radiately divided, and by its 
being covered with a hard shell, formed of numerous 
small pieces, placed on bands ; the animals also differ 
by the digestive canal being furnished with two distinct 
orifices, placed at some distance from each other. The 
shell is covered with moveable spines, which serve the 
animals as legs to walk with, and also enable them to 
bury themselves in the sand when they are left on the 
beach by the retreating tide ; it is likewise pierced with 
rows of minute pores, through which are emitted small 
tentacula with dilated ends, by which the animal is 
enabled 
