98 



INTRODUCTION TO ZOOLOGY 



CHAl>. 



decaying matter. Some, such as the " vinegar eels " and 

 " paste eels," have a wonderful power of withstanding desicca- 

 tion, so that they may be wafted about in the air a fact 

 that explains their apparently mysterious appearance at times 

 in weak vinegar or sour paste. 



PHYLUM VIII. : POLYZOA, SEA-MATS OK 

 CORALLINES 



These Polyzoans are nearly all marine colonial forms, and 

 many of them are common well-known objects of the sea- 



They are 

 mistakenly 



shore. 



often 



called Zoophytes,. 



though they are far 



removed from the 



true Coelenterate 



zoophytes (see p. 



23). 



Per- 



Flustra, the i ., 



Sea-mat. 



common- 

 est and best known 

 is the Sea - mat 

 (Flustra), which is 

 I B thrown up after 

 every storm on 

 (From some parts of our 

 coast, and soon looks 

 like a dry brown 

 seaweed. 



If obtained when first cast up, before it has dried, and then 

 examined in sea-water under the microscope, it will be found 

 to consist of a colony of individuals. Each has secreted 

 round itself a horny substance, which has hardened into a 

 little oblong cell, or " zooecium," decorated at each side with 

 short spines and having an opening at the upper end covered by 

 a little hinged lid. After a time, the tentacles of the creature 

 within may be seen gradually pushing up the lid. The polyps 

 are arranged in two layers, back to back ; so whichever surface 

 of the " mat " we look at, we get the same view of them. 



FIG. 51. The Sea-mat (Flustra foliacea). 

 the Cambridge Natural History.) 



A, Natural size, B' indicating the portion magnified in 

 B ; a, zooecium with closed lid. 



