712 COELENTERATAIL CNIDARIA. 



Another peculiarity of the Ctenophora is a sensory organ always found at 

 the end of the body opposite to the mouth. This somewhat resembles a 

 small weight borne on springs, and, as it i3 sensitive to the slightest oscilla- 

 tions of the body, seems to enable the animal to regulate its position in the 

 water. 



The Sea Gooseberry, depicted in Fig. 20, is a good example of a round 

 Ctenophoran, the swimming plates and long capturing filaments being well 

 developed. The best known of the ribbon-like forms is Venus's Girdle 

 (Cestus veneris). The mouth lies at the centre of the long, transparent 

 ribbon, which has no swimming plates, but is fringed with cilia. When 

 alarmed, this Ctenophoran can roll up either or both ends of its body 

 spirally, but, when undisturbed, passes through the water with a graceful, 

 undulating motion. Its iridescent colouring makes it a peculiarly lovely 

 object. Other Ctenophorans are barrel-shaped, or resemble Phrygian caps, 

 and many are beautifully phosphorescent at night. 



Most of the Ctenophora feed on small Crustaceans. Some, e.g., the 

 Beroidse, are very voracious, devouring creatures of their own kind, and often 

 larger than themselves, as the mouth is very wide, and the body distensible. 

 They have even been known to swallow and digest fish. 



All the Ctenophora multiply by means of fertilised eggs and ciliated larvae, 

 which only very gradually attain the adult form. 



