INTRODUCTION. 



IX 



which both the creeping stolon and the erect stems are 

 composed. Through the minute orifices in these plates 

 thread-like prolongations of the endosarc pass^ and esta- 

 blish a connexion between all the polypides in the colony. 

 The communication-plates vary in number, position, 

 and form ; they are furnished either with a single central 

 foramen* or with several minute pores arranged in diffe- 

 rent ways (Woodcut, fig. iv.). According to Nitschef, in 



Fig. iv. 



Zoohotryon. — Portion of stem. 

 cp. Gommunication-plate. p. Pores. 



the common Membranipora membranacea each normal 

 zooecium has generally twelve of these plates — two at each 

 extremity, and four in each side- wall. Those belonging to 

 each zooecium correspond with others in the adjacent 

 walls, so that the connecting-threads can pass directly 

 from cell to cell. Every zooecium in this species has two 

 openings into each of the six cells which abut upon it. 



Mr. Waters has drawn attention to the communica- 

 tion-plates as likely to afford good diagnostic characters, 



* As in BowerbanJcia imbricata, according to Joliet, ' Bryozoaires d. cotes 

 do France,' p. 31, note. 



t ' Beitrage zur Kenntniss der Bryozoen,' ii. Heft : " Ueber die Anatomie 

 n. Entwicklungsgesch. von Flusfra membranacea" Zeitscli. f. Wissenscb. 

 Zool. xsi. Band (1871). 4. Heft, p. 42. 



