190 



POLYZOA 



ribs, etc. The anterior part of the polypide can be 

 withdrawn by means of longitudinal muscles into the 

 zocecium, just as the finger of a glove can be pulled 

 into the hand. In some Polyzoa (the Cyclostomata, etc., 

 fig. 90 B) the zocecium is tube-like, the aperture is at the 

 end and is of the same diameter, or nearly so, as the rest 

 of the tube. In others (the Cheilostomata, fig. 90 A) 

 the zocecium is more or less oval, the aperture (?n) is 

 contracted and is not terminal, but is situated in front 

 near the anterior end, and is provided with a movable lid 



Fig. 90. A, Portion of Smittia landsborovi, a Cheilostomatous Polyzoan, 

 Kecent. o, ooecium ; m, aperture of the zocecium ; a, avicularium. B, 

 Portion of Tubulipora fimbria, a Cyclostomatous Polyzoan, Recent. 

 Enlarged. 



or operculum. In many of the Cheilostomata there is at 

 the anterior end of the zocecium, above the aperture, a 

 projecting chamber (o), termed the ooecium, into which the 

 ova pass. In many forms of Cheilostomata some of the 

 individuals are modified so as to form appendages termed 

 avicularia and vihracula. The avicularium (fig. 89 B) 

 may be sessile or placed on a peduncle (p), and in the more 

 specialized forms has somewhat the appearance of a bird's 

 head, consisting of a chamber (C) produced into a beak and 

 provided with a mandible (md) which is kept constantly 



