Distribution, Food and reproductive Capacity of some fresh-water Amphipods. 5 



rhizoids of Ricciocarpus, and the filaments of Chaetophora, Spi- 

 rogyra and certain blue-green algae. 



In early spring the amphipods Hyalella and Eucrangonyx often 

 congregate in large numbers in the prolific masses of Spirogyra. In 

 cases which came under observation, it was noticed that the animals 

 seemed to prefer dead bits of leaves and other plant remains which 

 occured in these masses, in place of the green algal filaments. 



Animal tissue constitutes not an unimportant element in the diet 

 of amphipods. Freshly killed isopods, snails, earthworms, tadpoles and 

 bits of tissue from fish, and of beef were greedily taken by young as 

 well as by adults. A freshly killed amphipod is readily devoured by 

 its fellows. 



Individuals of any one of the four species will viciously attack a 

 wounded Asellus. If one of the latter is slightly cut or torn the 

 exuding juices attract these Crustaceans in great numbers. They 

 pounce upon the wounded spot and in a short time tear the softer 

 parts of the body into shreads. Each amphipod pulls off a piece 

 and swims away with it. Even the whole carcass may be carried 

 away by an especially large one. The gnathopods and maxiUipeds 

 ordinarily are used for holding the food but in tearing off shreads of 

 tissue or in pulling one piece away from another amphipod, the use 

 of the mandibles in opposition to the gnathopods seems to be necessary 

 for success. Banta states (1907 p. 78) that in Mayfield's Cave, Indiana, 

 Eucrangonyx gracilis "sometimes feeds upon the cave isopod, Cae- 

 cidotea stygia. I have twice seen it in an aquarium catch a living 

 Caecidotea. It feeds upon any organic matter or even upon the car- 

 cass of a fellow". 



Several freshly crushed planaria were at different times offered to 

 individuals of each of the four species of amphipods but in every case 

 were refused. Whenever an amphipod came within the region polu- 

 ted by the body fluids of a planarian the former would instantly 

 jump away, indicating a disagreeable irritating property of the fluid. 



In July 1908, a sora rail which had been dead a day or two was 

 found floating in a marsh pool. Its feathers were alive with Hyalellas 

 which had been feeding upon the decomposing flesh. 



It has been stated that the cast off skins are sometimes devoured 

 and that these amphipods even prey upon one another. Those under 

 observation were frequently seen tearing to pieces their cast skins but 

 in no case was there convincing evidence that any portion of the latter 

 had been eaten. Only indirect evidence came to my notice tending to 



