64 



FLATWORMS AND MESOZOA, ETC. 



with its hundreds of swaying avicularia, and with its tentacular 

 funnels protruding from their zooecia, and withdrawing capriciously 

 from time to time. 



The Polyzoa, with respect to external form, may be roughly 

 divided into— (i) Encrusting forms, usually calcareous, but some- 

 times soft ; and (2) erect forms, which are either rigid or flexible. 

 This flexibility can co-exist with a highly calcified ectocyst, as in 



Fig. 1. — Bugula terminata, Alder, Plymouth. 



A, A small colony (natural size). B, Portion of a branch (x 50). 

 a. a'., Avicularia in different positions; ap., "Aperture" ; b, Poly- 

 pide-bud, attached by its stomach tob b., Brown body ; m., Mouth, 

 surrounded by the body of tentacles (two individuals to the right show 

 the tentacles partially expanded); 0., ovicell ; s., marginal spine. 

 The avicularia of some of the zooecia have been omitted in B. 



