COMB JELLY-FISH 



483 



Zucernaria, &c.) there is, on the contrary, no medusa stage 

 (fig. 296). 



LOCOMOTOR. 

 BAND 



Fig. 297.— Cydippe 



Class III.— COMB JELLY-FISH (Ctenophora) 



These are small, transparent, free-swimming forms occurring 

 in vast numbers in the open sea. When alive they are of 

 •extreme beauty. A common British genus, Cydippe, typically 

 exhibits the features of the class (fig. 

 297). 



Here the body may be compared in 

 shape to a minute melon, with the mouth- 

 opening at one pole and a complex sense 

 organ at the other. Locomotion is 

 brought about by eight longitudinal 

 bands of little paddles which suggest 

 the teeth of a comb. Each paddle is 

 apparently made up of a number of cilia 

 which have fused together. From each 

 side of the body a long feathery tentacle can be protruded, ^which 

 is used for the capture of food. These tentacles, when not in use, 

 are drawn back into pouches. The mouth leads into a gullet, and 

 that into a complex system of canals, which communicate with 

 the exterior by two pores at the opposite end of the body. 

 Nettling- cells are absent, but the tentacles are provided with 

 glutinous adhesive cells by which particles of food are secured. 

 There is no fixed stage in the life-history. 



Among other genera may be mentioned Venus s Girdle (Cestui), 

 in which the body is band -shaped and may be as much as a 

 foot in length; and Beroe, a cap-shaped form devoid of tentacles. 

 There are also two very interesting creeping genera [Ctenoplana 

 and Cceloplana), which, as a result of their mode of life (see 

 p. 23), present an approach to bilateral symmetry, and have 

 been compared to some of the Turbellarian worms (p. 445), it 

 even being suggested that the Turbellaria have been derived 

 from ancestral forms closely related to the Ctenophores. 



