VIII 



PHYLUM MOLLUSCOIDA 



315 



by the action of their cilia, the tentacles are prehensile as well as 

 tactile, and also act as organs of respiration. When retracted they 

 become enclosed by the walls of the introvert as by a sheath 



avic 



FIG. 255. Bugula avicularia. Two zooids, magnified, an. anus ; nV. avicularia ; oul. 

 embryo enclosed in the ocecium ; fu iiic. funiculus ; gout, muscular bands passing from the 

 stomach to the body wall ; int. intestine ; mo. mouth ; on. ocecium ; s. oesophagus ; or. ovary ; 

 ph. pharynx ; ret. parieto-vaginal muscles ; sp. spermatidia ; stom. stomach. 



the tentacle-sheath. A pair of bands of muscular fibres ihepaneto- , 

 vaginal muscles (ret.) passing to the introvert from the body- wall, 

 serve to retract the introvert and tentacles. 



