WILLIAD.E. 



Family WILLIAD^E Forbes. 



Williadce FORBES. British Naked-eyed Medusas, p. 19. 1848. 



Berenicidce AGASS. (p. p. non Esch.). Cont. Nat. Hist. U. S., IV. p. 345. 1862. 



WILLIA FORBES. 



TH/Ma FORBES. British Naked-eyed Medusae, p. 19. 1848. 

 Willia AGASS. Cont. Nat. Hist. U. S., IV. p. 346. 1862. 



Willia ornata McCu. 



Willia ornata MCR. Gymnoph. Charleston Harbor, p. 47, PI. 9, Figs. 9-11. 



Willia ornata AGASS. Cont. Nat. Hist. U. S., IV. p. 346. 1862. 



Willia ornata A. AGASS. ; in Proc. Bost. Soc. Nat. Hist., IX. Figs. 20, 21. 1862. 



The development of Willia presents some striking differences from 

 the mode in which tentacles are regularly developed in successive cy- 

 cles among Polyps, and from what has been observed, in accordance 

 with that mode of development, among some of our naked-eyed Me- 

 dusse (Laomedea diaphcma, Clytia bicophora, etc.). In very young 

 Willioe, having only four simple chymiferous tubes and four tenta- 

 cles, two much longer than the others, as we find them in Atractylis 

 and Lafoea, there are soon developed four additional tentacles ; these 



Fig. 274". Fig. 275. 



do not appear in the middle between the adjoining chymiferous tubes, 

 but about one third of the distance. (Fig. 274 a .) When this second 

 cycle of tentacles can be readily distinguished as four well-marked 

 knobs along the circular tube, an offset branches off from the sim- 

 ple chymiferous tube, which soon extends to the circular tube, oppo- 

 site the rudimentary tentacle ; this offset takes its origin at two thirds 

 the length of the chymiferous tube from the circular tube ; at the same 

 time this branch is forming, the main tube is slightly bent in the op- 

 posite* direction from that in which the branch diverges ; the offset 



Fig. 274 a . Youngest Willia observed, having only the second set of tentacles developed. 2, 

 second set of marginal tentacles ; 2e, branch of chymiferous tubes leading to them. 



Fig. 275. A young Willia, nearly in the stage of Fig. 276, seen from the abactinal pole. 3, 

 third set of tentacles ; 3 C , chymiferous tube leading to them. 



