ECHINODERMATA. 953 
backward so as to meet, we would have a very close imi- 
tation of a Sea-urchin, the ventral surface corresponding 
to the ambulacral areas. Echini live near the shore, in 
rocky holes or under sea-weed. They are less active than 
Star-fishes, but, like them, feed on Shells and Crabs. They 
reproduce by minute red eggs. 
Regular Echini, as the common Cidaris, are nearly 
globular, and the oral and anal openings are opposite. 
Irregular Echini, as the Clypeaster, are flat, and the anal 
orifice is near the margin. 
Crass [V.—Holothuroidea. 
These worm-like “Sea-slugs,” as they are called, have a 
soft elongated body, with a tough contractile skin contain- 
ing scattered granules. One end, the head, is abruptly 
terminated, and has a simple aperture for a mouth, encir- 
cled with feathery tentacles. There are five longitudinal 
Fig. 210,—Sea-slugs. (Holothuria). 
rows of ambulacral suckers, but only one is used for lo- 
comotion. The mouth opens into a pharynx leading to 
a long intestinal canal. Holothurians have the singular 
power of ejecting all their internal organs, surviving for 
some time the loss of these essential parts, aud afterward 
reproducing them. They occur on nearly every coast, 
