vii PHYLUM ECHINODERMATA 167 



The starfish is unisexual, each individual possessing 

 either ovaries (Fig. 88, ov) or testes, which appear very 

 similar until they are examined microscopically. They 

 consist of masses of rounded follicles, like bunches of 

 minute grapes, a pair in each inter-radial interval. The 

 ducts, by means of which the ova, or sperms, reach the 



Fig. 91. — Anthenea. View of dorsal surface. (After Sladen.) 



exterior, open on the dorsal surface (Fig. 88, A, Ova') 

 through a number of perforations on a pair of sieve-like 

 plates, situated inter-radially close to the bases of the arms. 

 Other starfishes, while resembling Asterias in most re- 

 spects, differ from it in a number of less important points. 

 Thus though the number of arms is usually five, in some 

 species it is eight, in others more, and in some of those with 



