112 WORMS, MOSS-POLYPS, SPONGES, ETC. 



Other encrusting forms, but with the pores or 

 cells arranged in only a single tier, are the ' sea- 



'^\ 



^. 



Membkanipoka (magnified). Polypide (magnified). Alcyonidium. 



mats,' which are usually found on the fronds of the 

 sea-weed. One of these (Membranipora) makes 

 small scale-like patches, while another (Flustra) 

 occurs in ramifying or spreading branches. A less 

 readily recognizable form of polyzoan, the Alcyo- 

 nidium, making fleshy crusts a third of an inch or 

 more in thickness, is frequently 

 found enveloping small stones, 

 twigs, etc. 



While perhaps the most distinc- 

 tive polyzoans are the ones which 

 make crusts like those above de- 

 scribed, others grow in erect, 

 branching colonies, and thus still 

 more closely resemble the swaying 

 fronds of the true polyps. One of 

 these is the common Bugula, whose 

 tree-like forms, bearing tiny cups 

 on their upright branches, strongly recall the ser- 

 tularians or sea-firs. They are of particular interest 

 to the microscopist since they show to special ad- 



BUGULA. 



