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THE AMERICAN NATURALIST [Vol. XLT1 



traveled in the opposite directions, against the currents, 

 unless by human agency, in recent times. 



Many Crustacea, including the higher and more active 

 forms, especially the grapsoid and cancroid crabs, are in 



the habit of hiding among the clusters of barnacles, etc., 

 attached to the bottoms of vessels, and in this way they 

 may be carried across the oceans in any direction, so long 

 as the temperature of the water is suitable for their exist- 

 ence. In this way many tropical species reach the New 

 England coast in summer, but die out during the winter. 



Severn] species of crabs and shrimps habitually live 

 among floating sargassum, or attached to floating drift- 



