POLYZOA 



189 



mentary canal and the body-wall is a spacious body-cavity. 

 The nervous system consists of a single ganglion (g) placed 

 on the side of the oesophagus facing the intestine. The 

 polyzoa multiply by budding and sexually, and are gene- 

 rally hermaphrodite. Heart and blood-vessels are absent. 



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Fig. 89. A, Diagram of the structure of a single Polyzoan individual. 

 s, body- wall; t, tentacles; o, mouth ; oes, oesophagus; st, stomach; 

 int, intestine ; a, anus ; g, ganglion ; /, funiculus ; ov, ovary ; sp, 

 testis. B, Avicularium of Bugula, enlarged, b, beak; md, mandible; 

 C, chamber ; p, peduncle ; om, occlusor muscles ; dm, divaricator 

 muscles. (After Hincks.) 



The structures described above form together what 

 is known as the polypide ; this is contained in the body- 

 wall or zooecium. The outer layer of the zooecium, known 

 as the ectocyst, generally becomes hardened by calcareous 

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

 alone remains ; its surface is usually ornamented with 



