PHYLUM CTENOPHORA 



159 



tentacular pouches connected with the outside ; one lies on each side 

 of the infundibulum. The solid prehensile tentacles emerge from 

 these sacs. 



Around the aboral surface of the body- is a collection of sense 

 structures or statocysts, which serve as organs of equilibrium by 

 stimulating- the cilia of the bands on the side against which the in- 

 ternal calcareous ball (statolith) rolls as the level of the body changes. 

 These animals are monoecious (hermaphroditic) ; the ova are formed 

 in ovaries along one side of each meridional canal and spermatozoa 



Fig. 77. — Sea walnut or comb jeUy, Beroe ovata, from Atlantic Ocean and Gulf of 

 Mexico. (Courtesy of General Biological Supply House.) 



along the other. The mature germ cells rupture into the infundibu- 

 lum and pass through the stomodeum to the exterior. The fertilized 

 ovum develops and finally metamorphoses to the adult stage. There 

 is no alternation of generation. The animals are triplohlastic instead 

 of diploblastic as are Hydras, because, instead of a simple mesogloea, 

 there are, in addition, differentiated muscle fibers lying between the 

 ectoderm and endoderm. This is a morphological advance when com- 

 pared to the coelenterates. These animals have no nematocysts and 

 therefore do not irritate bathers as do jellyfish, but they do serve as 

 food for a large number of valuable fish. Otherwise they have no 

 economic importance. 



