Echinodermata. 



337 



Development of the Starfish. The female has a pair of 

 ovaries at the base of each ray. They are like slender 

 bunches of tiny grapes. The eggs pass out of minute pores 

 in the angles between the bases of the rays. In the males 

 the spermaries occupy a similar position and resemble the 

 ovaries in form, but are lighter colored, usually white. The 

 young starfish goes through a remarkable transformation, 

 the young no more resembling 

 the adult than in the case of 

 many insects with which we 

 are familiar. The most strik- 

 ing fact is that the young is 

 very distinctly bilaterally sym- 

 metrical, showing no traces of 

 radial symmetry. 



Other Forms of Starfishes. 

 Most starfishes are five-rayed, 

 but in some the rays are so 

 short that the whole animal is 

 a pentagon, the rays hardly 



extending beyond the disk. Some are brilliant, exhibiting 

 beautifully complementary colors of purple and orange. 

 The number of rays may be as many as twenty. A Pacific 

 starfish sometimes becomes two feet in diameter. 



FIG. 190. 



BRITTLE STAR; SAND 

 STAR. 



CLASS II. OPHIUROIDEA. 



The Brittle Stars. The ophiuroids are represented by 

 the brittle stars. Their general form is similar to that 

 of the starfishes. But the central disk is more distinct and 

 the arms relatively slender. The arms are more flexible 

 and the brittle star locomotes by active lateral movements 

 of the arms, making rapid progress compared to a starfish. 



