70 
room x. 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 uniform structure with it. Most of 
the species have the faculty of reproducing the 
arms, or such parts of them as may be accident¬ 
ally broken off; and if an entire arm be sepa¬ 
rated, provided a part of the body be attached 
to it, other arms are reproduced, and a perfect 
fresh animal is formed. Some specimens illus¬ 
trative of these facts are in the Case No. 10. 
The Asterise differ greatly 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 di¬ 
vided, and by its being covered with a hard 
shell, formed of numerous small pieces, placed 
on bands; and the animals differ by being pro¬ 
vided with two distinct and distant openings to 
the digestive canal. The shell is covered with 
very moveable spines, which serve the animals 
as legs to walk with, and also enable them to 
bury 
