104 DIPHYIDJE. PART m. 



one end of the long tubular filiform body of the animal 

 is fixed by slender tubes, through which a nourishing 

 liquid passes into radiating canals in the bells, and from 

 them into a circular canal at their margins, which are 

 surrounded by a muscular contractile iris, like that in our 

 eyes, which shuts and opens the bells. By the alternate 

 absorption and ejection of the water the bells go head 

 foremost, and regulate the motions of the whole com- 

 pound animal. When both bells are active it goes 

 straight forward ; when the right hand bell is alone in 

 action, it goes to the left, and vice versa; in fact, the 

 bells act as a rudder. 



The slender cylindrical body or axis of the Praya is 

 so transparent, that the cavity and muscular fibres of its 

 walls are distinctly seen. These animals are extremely 

 contractile. Professor Yogt mentions an individual he 

 met with at Nice more than three feet long, when ex- 

 tended on the surface of the water, which could contract 

 itself into little more than a finger length. It was said 

 to have had a hundred isolated groups of polypites with 

 their appendages attached to it; but in general the 

 Prayse are not so long, and seldom have more than thirty 

 or forty of these isolated groups, which are attached to 

 the under-side of the long flexible body, and hang down 

 like a rich and beautiful fringe. In the figure, the po- 

 sition of the numerous groups of polypites and their ap- 

 pendages are merely indicated by round marks and lines. 



In the body of the Praya diphys (fig. 117), as in that 

 of the whole family, there is a nutritious liquid, which, 

 by means of cilia, flows on its interior surface in two 

 directions : it enters the canals in the two large bells, 

 and supplies them with nourishment. 



The polypites which digest the food are vermiform 

 double sacs communicating at one end by a valve with 

 the canal in the body of the animal ; and at the free 

 end they are prolonged into a mouth with an everted lip, 



