i 5 8 MANUAL OF ZOOLOGY SECT. 



completely rigid in the fresh condition r but presents a 

 certain limited degree of flexibility. The body (Fig. So) 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 upwards in the natural position of the 



FIG. 80. Starfish. General view of the ventral surface, showing the tube-feet. 

 (From Leuckart and Nitsche's Diagrams.) 



living animal ; the other, the ventral, or actinal, directed 

 downwards. The dorsal surface 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. 86) is a five- 

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

 a radiating manner are five narrow grooves, each passing 



