RADIATA. 



83 



pores, Millepores, and Gorgonidae work chiefly at the 

 top, next below we meet with Meandrinas, and lowest 

 of all, with Astraeans. 



The Ctenophorce, or comb-bearing Medusae, exhibit 

 traces of a nervous system in a ganglionic mass at the 

 upper end, or pole, of the animal, with nervous filaments 

 radiating to every part of the body. They are trans- 

 parent gelatinous animals, which swim freely by means 

 of bands of comb-like fringes or paddles. Their internal 

 structure is quite complex, having a distinct alimentary 

 canal, and ducts for the circulation of fluid. They are 

 retained in the Radiate type, on account of the radiate 

 arrangement of the bands of cilia and the presence of 

 urticating organs on the tentacles, although their affini- 

 ties would seem to place them elsewhere. 



The Beroe and Cydippe (Fig. 85) and Cestum Veneris, 



FIG. 85. A. Cydippe pileus, with its tentacles extended. B. Beroe Forskalii, showing 

 the tubular prolongations of the stomach. 



or Girdle of Venus, belong to this order. In the latter, 

 the sides are prolonged into a ribbon, although the 

 mouth and digestive organs are confined to the middle 



