74 



PELAGIC FAUNA 



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A ctenophore (Ctenoplana) which can both crawl and swim, drawn on board from life. 



the colony with their stinging cells and catch its food. Some of the colo- 

 nies are kept afloat by means of a small oil receptacle, while others have 

 a small bladder of gas at the summit. Unfortunately, the colonies nearly 

 always break up into their component parts when removed from the water. 

 Most of them occur at all levels, but three species are so full of gas that 

 they drift on the surface, where they are a familiar sight to all who sail 



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By-the- wind-sailor (Velella). 



