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MANUAL OF ZOOLOGY 



torn away by the struggles of the captured prey. An allied 

 form is Pleurobrachia, very abundant off our shores. 



In some of the Ctenophora the body is produced into a 

 pair of lateral lobes. In Beroe, instead of being globular, it 

 is more nearly cylindrical, with an extremely wide mouth 

 and gullet, and without tentacles. In 

 the " Venus's girdle" (Cesfus), it is 

 compressed and almost ribbon- like. 

 All are free-swimming ; colonies are 

 never formed ; and there is never any 

 kind of skeleton. 



The Ctenophora are usually per- 

 fectly transparent, and quite colour- 

 less, save for delicate tints of red, 

 brown, or yellow on the tentacles or 

 on ridges on the inner surface of the 

 gullet. Cestus has, however, a deli- 

 cate violet hue, and, when irritated, 

 shows a beautiful blue or bluish-green 

 fluorescence ; while Beroe is coloured 

 rose-pink, and Idyia is of a brilliant pink. The most 

 primitive form to be found on our coast is Idyia (Fig. 67), 

 which is a simple oval sphere, the interior of which forms an 

 immense digestive cavity, in which entire large animals may 

 be engulfed. 



Fig. 67. — Idyia roseola. 



Seen from the broad side, 

 half natural size, a, anal 

 opening", /», lateral tube; c, 

 circular tube; d, e, f, g, h, 

 rows of paddles. ( After 

 Agassiz.) 



