CTENOPHORA. 254 
tentacles, much longer and coloured red ; itis about the,size of a 
hazel-nut, and phosphorescent. Within the clear substance of the 
LPleurobrachia, 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 
