THE WILLSIA AND ITS PARASITE. 359 



THE STARRY WILLSIA. 



Sept. Si h. — In the clear quiet water of the hathing 

 pool I dipped this afternoon many Medusae, almost 

 all of these two species, Tliaumantias pilosella and 

 Willsia stellata. One of the former presented a curi- 

 ous deviation from ordinary structure, in that one of 

 the radiating vessels was divided into three branches 

 at about one third of its length from the marginal 

 canal, the ovary likewise branched correspondingly. 

 The other vessels were quite normal. 



Less numerous than this, but sufficiently common, 

 was the pretty Willsia, a little gem, with its six-rayed 

 star of vellow ovaries, and its circlet of black eyes. 

 (Plate XX, fig. 1). The radiating vessels in this 

 species, six in number, are naturally divided into 

 branches, each entering the marginal canal by four 

 mouths, like the Delta of some great continental river. 

 The sub -umbrella is not evenly round, but lobed, 

 the radiating vessels running along deep depressions 

 or valleys, between which the surface rises into hills. 

 (See fig. 2). 



I found in one of the Willsice a curious parasitic 

 Leech. I know not on what part, for I first discover- 

 ed it after I had subjected the Medusa to the compres- 

 sorium. It is an active little animal, with two suck- 

 ers, of which the anterior is imperfect and mouth-like, 

 and the posterior is circular, produced into a thick 

 wart, and set on the ventral surface at about one 

 third of the whole length from the tail. There are eight 



