POLYZOA. 



103 



the circle of tentacles. On account of this approximation 

 of the mouth and anus the alimentary canal is bent into a 

 U-shape, and in it may be distinguished oesophagus (ces), 

 stomach (st) and intestine (int). Between the alimentary 

 canal and the body wall there is a considerable space, 

 filled with fluid, this is the body-cavity or coelom. The 

 nervous system consists of a single ganglion (g) placed 

 on the side of the oesophagus facing the intestine. The 

 polyzoan multiplies sexually and by budding; generally 

 the polypide is hermaphrodite, the ovary and testie occur- 

 ring in the same individual. Blood vessels and excretory 

 organs are absent in almost all forms. 



The outer layer of the body wall in the lower part of 

 the polypide generally becomes hardened by calcareous or 

 chitinous matter, and after the death of the animal, this 

 alone remains, constituting the zocecium. The zocecium 

 therefore is not distinct from the body wall, but is merely 

 its outer hardened layer. The anterior part of the poly- 

 pide can be withdrawn by means of longitudinal muscles 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 



FIG. 28. A, Portion of Si Mia landslorovi, a Cheilostomatous Polyzoan, 

 Recent, o, ocecium m, aperture of the cell; o, avicularium. 

 B, Portion of Tubulipora fimbria, a Cyclostomatous Polyzoan, 

 Recent. Enlarged. 



