148 ANIMAL FORMS 
the power of locomotion. In some of the sea-cucumbers 
five equidistant rows of tube-feet extend from one end of 
the body to the other, and the animal crawls worm-like 
upon any side that happens to be down; but certain spe- 
cies living in the sand, 
where tube - feet will 
not work satisfactorily, 
have lost all traces of 
them, and creep like an 
earthworm from place 
“,,' to place. In all the 
“y —_sea-cucumbers the feet, 
situated nearthe mouth, 
have been curiously 
Fie. 94.—An unattached crinoid (Antedon). One- modified to form a vile 
half natural size, clet of tentacles, which 
range in form from 
highly branched to short and thick structures, and in func- 
tion from respiratory organs and those of touch to con- 
trivances for scooping up sand and conveying it to the 
mouth. 
141. Food and digestive system.—In the echinoderms the 
body-wall is comparatively thin (Fig. 95), and encloses a 
great space, the body-cavity, in which the digestive and re- 
productive organs are contained. As the former in various 
species is adapted for acting upon very different kinds of 
food, it shows many modifications; but there are a few prin- 
cipal types which may be briefly considered. 
In the starfishes the mouth enters almost directly into 
the cardiac division of the stomach, a capacious, thin-walled 
sac, much folded and packed away in the disk and bases of 
the arms (Fig. 95, 6). This in turn leads into the second 
pyloric portion (a), with thicker walls and dorsal, to the 
first, from which a short intestine leads to the exterior, 
near the center of the disk. Another conspicuous and im- 
portant feature is the so-called liver, consisting of a pair 
