VIBRACULA ENTOPROCTA 



487 



wanting, and it must be admitted that the subject needs further 

 elucidation. 



The vibracula ordinarily remain stationary for some little 

 time, every now and then giving a sweep through the water. In 

 the majority of cases these structures, like the avicularia, act 

 perfectly independently of one another, so far as can be made 

 out; but in Cdberea (Fig. 242) the vibracula move in unison, 

 the simultaneous action of the whole series, after a period of 

 quiet, being described as " positively startling." l 



It has been stated by Busk 2 that the entire colony in Selen- 

 aria and Lunulites may be moved from place to place by the 

 large vibracula which these forms possess. 



Entoprocta. The Entoprocta, although a very small sub- 

 class, deserve special consideration, if for no other reason, from 



5 



3 



FIG. 243. Pedicellina cernua Pall., Guernsey. Entire colony, x 27. The colony has 

 three growing ends, a; 1-8, individuals of colony ; 1 and 8 are quite immature ; 

 and 7 (tentacles retracted) is still young ; 2, is seen in longitudinal section ; g, 

 generative organ, and below it the ganglion ; m, mouth ; r, rectum ; , stomach ; 

 between g and r are three embryos in the brood-pouch ; the tentacles are retracted ; 

 in 5 and 6 the tentacles are expanded ; in 6 two embryos are seen within the circle 

 of the tentacles, to the left of them is the rectum, and to the right the mouth ; 8 

 is in the act of losing its calyx, and has already developed the beginning of a new 

 polypide-bnd ; in 4 the primary calyx has been lost, and the new calyx is clearly 

 marked off from the stalk. 



the fact that many writers regard them as the most primitive 

 group of Polyzoa, and consequently as the forms which show 

 most affinity to other classes of animals. 



Their most obvious characteristic is, as we have already seen, 8 

 the position of the anus within the circle of tentacles. The 

 individuals formed by budding always remain more separate from 

 one another than those of most Ectoprocta. 



1 Hincks, Brit. Mar. Polyzoa, i. p. 58. 

 2 BrU. Mus. Cat. part ii. 1854, p. 106 ; Hincks, t. cit. p. 181 n. 



p. 475. 



