POLYPIDOMS. SEA PENS, ETC. 193 



multitude of individuals, a single specimen some- 

 times containing five or six thousand individual 

 polypes, and some of the species, known as Ser- 

 tularia argentea, being formed of eighty or ninety 

 thousand, all united together by the medullary 

 substance or fibre contained in the branches. 

 Numerous specimens of this kind are often found 

 fixed upon a single sea-weed, which would thus 

 afford an abode to a population greatly more 

 numerous than the most populous city in the 

 world. 



The Sea Pen is by no means a rare object on 

 many of our coasts. It belongs to the family of 

 polypes, and is compound, consisting of nu- 

 merous individuals united. The Pennatula phos- 

 phorea may often be met with, and is extremely 

 remarkable. It is three or four inches in length, 

 of a purplish red colour, and fleshy in substance, 

 and like a pen naked at one extremity and 

 feathered on the other, with closely-set pinnae, on 

 the edges of which are the cells of the polypes. 

 The body of the common stalk and branches, or 

 pinnae, is calcareous, and thus possesses the requi- 

 site degree of strength. The sea pen is phospho- 

 rescent, and when irritated or injured or thrown 

 into fresh water the polypes shed a brilliant light. 

 The Sea Fans are of the same order. The 

 Gorgonia flabellum is a well-known West Indian 

 species, called Venus's fan, but it has occasionally 

 been found apparently cast ashore on the British 

 coasts. One of the British species of sea fans -is 

 common on the shores of Devonshire, and is 

 o 



