WILLIAD^E. 



171 



Family WILLIAD^E Forbes. 



Willinilfc Forbes. British NakiuU-yed Mi'dusae, p. 19. 1848. 



Berenicidce Agass. (j>- p- non Esch.). Coat. Nat. Hist. U. S., IV. p. 345. 1862. 



WILLIA Forbes. 



WUlsia Forbes. British Naked-eyod Mt-dusjc, p. 19. 1848. 

 Witlia Agass. Cont. Nat. Hist. U. S., IV. p. 346. 1862. 



Willia ornata McCr. 



Willin nrnnin McCr. Gymiiopli. Charleston Harbor, p. 47, PI. 9, Fio;s. 9-11. 



Willia nrniita Agass. Cont. Nat. Hist. U. S., IV. p. 34(;. 1862. 



Willia ornata A. Agass. ; in Proc. Best. Soc. Nat. Hist., IX. Fips. 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 ol)servcd, in accordance 

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

 dusse {Laomedea diaphana, Clytia bicophora, etc.). In very j'oung 

 Willi^e, 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 



Fiff. 274". 





Fi?. 275. 



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

 but about one third of the distance. (Fig. 27•i^) 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 chvmiferous 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 wdiich the branch diverges ; the offset 



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

 second set of maro;inal tentacles ; 2c, 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 ^ 3c, chymiferous tube leading to them. 



