158 MANUAL OF ZOOLOGY SECT. 



fresh condition, but presents a certain limited degree of 

 flexibility. The body (Fig. 86) is star-shaped, consisting of 

 a central part, the central disc, and five symmetrically 

 arranged processes, the arms or rays t which, broad at the 

 base, taper slightly towards their outer extremities. There 

 are two surfaces, one the dorsal or abactinal, directed up- 



FlG 86. Starfish. General view of the ventral surface, showing the tube-feet. 

 (From Leuckart and Nitsche's Diagrams.) 



wards in the natural position of the living animal ; the other, 

 the ventral or actinal, directed downwards. The dorsal sur- 

 face is convex, the ventral flat ; the colour of the former is 

 much darker than that of the latter. 



In the centre of the ventral surface (see Fig. 92) is a five- 

 rayed aperture, the actinostome, and running out from this in 

 a radiating manner are five narrow grooves, each running 

 along the middle of the ventral surface of one of the arms 



