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 

 sea-cucumbers the feet, 

 situated near the mouth, 

 have been curiously 

 modified to form a cir- 



FIG. 94. An unattached crinoid (Antedon). One- . 



half natural size. clet OI 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, ). This in turn leads into the second 

 pyloric portion (#), 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 



