i 5 S 



MANUAL OF ZOOLOGY 



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, which, broad at the 

 base, taper slightly towards their outer extremities. There 

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



FlG. 



-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 



