BRYOZOA. 



FIQ. 667. 



437 



Bryoza, CeUularia avicularia. 



a, natural size of a growing cluster; b and c, portions much magnified; d, bryo- 



zoan in its cell. 



species every cell has its " birds' head " (Fig. 667), and 

 this structure is exceedingly active, opening, shutting, and 

 snapping almost continually. 



Many of the marine kinds produce coral ; and patches 

 of this substance are common on stones, shells, and 

 sea-weeds. These delicate patches of coral are composed 



