STAR-FISH. Ill 



with these forks, little Crustacea, for instance ; but this is prob- 

 ably not their only office. The Star-fish has a fourth set of 

 external appendages in the shape of little water-tubes. (Seen in 

 Fig. 143.) The upper surface of the back consists of a strong 

 limestone network (Fig. 144), and certain openings in this net- 

 work are covered with a thin membrane through which these 

 water-tubes project. It is supposed that water may be intro- 

 duced into the body through these tubes ; but while there can be 



Fig. 144. 



no doubt that they are constantly filled with water, and are 

 therefore directly connected with the circulation through the 

 madreporic body (Fig. 145), no external opening has as yet been 

 detected in them. The fact, however, that when these animals 

 are taken out of their native element, the water pours out of them 

 all over the surface of the back, so that they at once collapse and 

 lose entirely their fulness of outline, seems to show that water 

 does issue from those tubes. The ends of the arms are always 

 slightly turned up, and at the summit of each is a red eye-speck. 

 The tentacles about the eye become very 

 delicate and are destitute of suckers. 



These animals have a singular mode of 

 eating ; they place themselves over what- 

 ever they mean to feed upon, as a cockle- 

 shell for instance, the back gradually 

 rising as they arch themselves above it ; 

 they then turn the digestive sac or stom- 

 ach inside out, so as to enclose their prey 



Fig. 143. Single spine of Star-fish, with surrounding appendages ; magnified. 

 Fijy. 144. Limestone network of hack of Star-fish. 

 Fig 145. Madreporic body of Star -fish } magnified. 



