INTEODUCTION-. 9 



areas, each of which represents one individual of the colony or 

 (to use Proudho's term) a Bryozoite. If we separate one of the 

 Bryozoites from the colony (or zoarium), we find it consists of a 

 double-walled cell (or zooecium}, and of a zooid which lodges 

 within it. 



FIG. 1. Diagram of structure of typical Bryozoa. an. anus; ap. aperture; 

 b.c. body cavity ; c.p. communication pore ; d. diaphragm ; ect. 

 ectoderm ; end. endoderm ; /. f uniculi ; n. nerve ganglion ; o. orifice ; 

 oss. oesophagus; op. operculum; r.m. retractor muscle; st. stomach; 

 T. tentacles ; t.s. tentacle sheath. 



The zocecium is the skeleton or shell in which the zooid lives ; 

 but it was at one time believed to be an independent individual, 

 modified for protective purposes. This view, however, is now 

 known to be erroneous ; the zocecium and zooid together form an 

 individual Bryozoite, just as an oyster and its shell together form 

 an individual Mollusc. The zooid consists, essentially, of a closed 

 digestive tube, shaped somewhat like a fish-hook with the curved 

 part greatly thickened. The longer arm begins with a funnel- 

 shaped oesophagus, at the top of which is the mouth ; the shorter 

 arm ends with the anus. The expansion at the curve is the 

 stomach. The mouth (or " orifice") is surrounded by a circle of 

 ciliated tentacles, which form the structure known as the " lopho- 

 phore." There is one small nerve ganglion beside the mouth, 

 situated between it and the anus. The zooid lives either crowded 

 into the cell-like zooecium, or rising from it with its tentacles 

 expanded. The space between the zooid aud the wall of its 



