228 TBANSAOTIONS OF THE [1892 



The most accessible prey of the Patapsco colonies appears to be a 

 small species of Water Flea, which, during the summer months, also 

 abounds among the stems of the colonies. These are readily swallowed, 

 but the dimensions of a larger species of crustacean which they are able 

 to capture, are such that the hydroids are compelled to devour them 

 gradually, as in the case of the above-mentioned insect larva. 



At Fort Covington I have at certain seasons seen attached to the stems 

 and branches of the colonies large numbers of tubular cells, constructed 

 by small crustaceans (not unlike the smaller water fleas just mentioned), 

 which also serve as food. Here, too, the beautiful colonies of Vorticella, 

 which grow upon the stems in great profusion during the early summer 

 (p. 220), probably contribute to the food supply. 



Bai.timork, Nov. 7, 1893. 



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