CTFNOPHORA. 



251 



tentacles, much longer and coloured red ; it is about the size of a 

 hazel-nut, and phosphorescent. Within the clear substance of the 

 Pleurobrachia, on each side of the stomach, there is a capacious 

 cavity, which communicates with the surface, and within each cavity 

 is fixed the tentacle, of great length, and very slender, which the 



Fig. 103. Cestum veneris (Lesueur). 



animal can at pleasure shoot out of the orifice and suffer to trail 

 through the water, shortening, lengthening, twisting, twining, or con- 

 tracting it into a tiny ball at will, or withdrawing it into its cavity, 

 short filaments being given off at intervals over the whole length of 

 this attenuated thread-like apparatus, each of which can also be 

 lengthened or shortened, and coiled individually. These proceed 

 only from one side of the thread-like tentacle, although, at a casual 



