WILLIADiE. 



171 



Family WILLI ADiE Forbes. 



U'/V/i'drffE Fouhes. British NakiHl-evcd iModusa;, ]). U). 1818. 



BareiticidcE AuASS. (j)- })■ non Esch.). Cunt. Nat. Hist. U. S., IV. p. 345. 1862. 



WILLIA Forbes. 



TriW.s-w Forbes. British Naked-eyed Meilusa;, p. 19. 1848. 

 Wtllia AG.A.SS. Coiit. Nat. Hist. U. S., IV. p. 34«. 1862. 



Willia ornata McCr. 



WlUin ornata McCr. Gymnoph. Charleston Harbor, p. 47, PI. 9, Figs. 9-11. 



Willia ornata Ag.\ss. 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 regnlarly developed in snccessive cy- 

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

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

 dusas {Laomedea diaphana, Clytia hicojihora, etc.). In very young 

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

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

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



Fig. 274». 



Fig. 2T5. 



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

 but about one third of the distance. (Fig. 274^) 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*. Youngest Willia observed, having only the seeond set of tentaeles developed. 2, 

 -seeond set of marginal tentaeles ; 2c, braneli of ehyniiferous tubes leading to them. 



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

 third set of tentaeles ; .%, chymiferous tube leading to them. 



