12 CCELENTEBATA AND 



nient about the polar mouth opening. It was that radial 

 symmetry which Cuvier first recognized and which led 

 him to unite these animals with others in the group of lln- 

 diata. 



The Coelenterata include the Medusae and Actinias. While 

 these animals have much in common in their anatomical 

 structure, their external resemblances are oftentimes very 

 distant. Compare, for instance, the filmy, gelatinous 

 body of the jellyfish and the hard, stony coral as we see 

 it in our museums. Yet the calcareous and other hard 

 secretions of the body of the coral once removed, the soft 

 parts which remain betray anatomical peculiarities of the 

 stomach and body cavity already mentioned, and therefore 

 close resemblances to jelly-fishes. 



The Coelenterata are divided into the Hydrozoa, Cteno- 

 phora and the Actinozoa. The two former groups, known 

 as the jelly-fishes, are well represented by their larvae in 

 the surface waters of New England, while only a few forms 

 of the latter occur, or come within the scope of this ac- 

 count. While the larvae of some Actinozoa inhabit the 

 surface waters, there are few genera in Narragansett Bay 

 as compared with the other groups. 



CLASS I. HYDKOZOA AND CTENOPIIORA. 



{Jelly-fishes.') 



These animals have hyaline, gelatinous bodies ; live soli- 

 tary or united in colonies; bodies bell-shaped, tubular, 

 mushroom-like, cup-shaped, or resembling a floating bag 

 or disk. "When bell-shaped, a fleshy protuberance of 

 folded membrane hangs down from the under side and 

 serves as the stomach. The centre of the body is occu- 

 pied by a cavity out of which slender tubes or vessels ra- 

 diate to the bell- margin. These vessels may be united by 

 a circular tube about the periphery or may end blindly 



