THE SEA-ANEMONE AND SOME ALLIES 271 



The body of the comb-jelly is soft like that of the jellyfish, 

 but the plan of structure and the organs are somewhat differ- 

 ent. There are eight meridional bands of comb-like struc- 

 tures, which serve the animal as locomotor organs. During 

 locomotion these combs move vigorously, and in such a way 

 that beautiful iridescent effects are produced by them. 

 Near the lower end, as shown in the figure, there are two 

 fringed tentacles with such wonderful powers of extension 

 that from a mass no larger than a pin-head they can extend 

 over a foot. The tentacles have minute adhesive cells which 

 are thought to be .modifications of nettling-capsules, or struc- 

 tures which take the place of them. By means of the adhe- 

 sive cells the tentacles hold small animals and pass them to 

 the mouth. As the animal swims the tentacles are below 

 and the mouth above. A funnel-shaped space at the upper 

 end carries the food into the mouth. The gastro vascular 

 cavity extends into two lateral pouches from which two 

 branches arise, making four; each of the four branch-tubes 

 gives rise to two, making eight altogether. Each of the eight 

 branch-tubes joins a meridional tube which lies just beneath 

 the bands of combs. Food carried in at the mouth can thus 

 pass to any portion of the body. At the end opposite the 

 mouth there is a small sense-organ, which is the center of 

 the animal's nervous system. Every comb-jelly contains both 

 egg-cells and sperm-cells. The eggs are fertilized outside the 

 body, and the young larvae swim free and gradually develop 

 into the adult form. The comb-jelly produces a phosphor- 

 escent light when disturbed. 



The class of which Pleurobrachia rhododactyla is a repre- 

 sentative is called Ctenoph'ora (Gr. Jcteis (Jcten), comb; phero, 

 bear). 



Definition of Coelentera (Gr. koilos, hollow ; enteros, intes- 

 tine). Arranged in the order of their increasing degree of 

 specialization, the four classes that make up the phylum 



