128 MANUAL OF ZOOLOGY SECT, iv 



In the interior of the cell is a spirally coiled filament, the 

 delicate inner end of which can be traced to the muscular axis 

 of the tentacular branch. These spiral threads act as springs, 

 and tend to prevent the adhesive cells from being torn away 

 by the struggles of the captured prey. 



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 " 

 (Cestus), 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 perfectly transparent, and 

 quite colourless, 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 delicate violet hue, and, when 

 irritated, shows a beautiful blue or bluish-green fluorescence ; 

 while Beroe is coloured rose-pink. 



