BIOLOGY OF PHYSA 69 



the skeleton. Even the smallest veins and veinlets are left 

 intact so that an excellent method of obtaining skeletonized 

 leaves is to place them in an aquarium with hungry Physa. 

 Lymnaea eats not only the pulp but much of the fine vascular 

 system of the leaf as well. This difference is due perhaps to " 

 a difference in the jaws in the two species : the jaw of Physa is simple 

 while that of Lymnaea is composed of one upper and two lateral 

 pieces. It is no uncommon sight to see a water soaked leaf 

 floating near the surface of the water buoyed up by a number 

 of Physa which are feeding upon its pulp. This leaf raft is 

 unique in that the animal is supplied at once with air and food 

 as it crawls about on the surface of the leaf. Physa, Lymnaea 

 stagnalis, L. palustris and L. reflexa greedily eat both stale 

 and fresh meat. Planorhis trivolis and P. tricarnata are vege- 

 table feeders, at least they have never been induced to eat meat 

 in the laboratory. 



All of these flesh-eating snails have been seen eating dead 

 houseflies, Mayflies, fish, beefsteak and snails. They will eat 

 such meat fresh, although they seemingly prefer it stale. I 

 have seen them eating dead snails, when the odor from the food 

 could scarcely be endured in the laboratory. The Lymnaea 

 cited above have cannibal traits, a character which is especially 

 noticeable in L. stagnalis. I have seen this species devouring 

 struggling flies, moths and young snails that have become en- 

 tangled in its slime. It also attacks and eats its injured mates, 

 leaving nothing but the shell. These observations upon the 

 food habits of Lymnaea verify many similar observations of 

 other writers. Semper (1874) observed Lymnaea stagnalis 

 eating a live newt {Triton taeniatus) although vegetable food 

 was easily -accessible. Ullyett (1886) records its overpowering 

 and devouring healthy specimens of the common stickleback 

 in an aquarium. Baker (1902) found Lymnaea palustris feeding 

 upon the carcasses of cats and dogs. Walter (1906) says: 

 " The writer also observed that a dozen or more specimens of 

 Physa sp. confined in a glass of water with a few amphipods 

 (Gammariis sp.) in three days devoured the crustaceans, shell 

 and all." In this case however, there is no evidence that the 

 crustaceans were killed by the snails. I have never seen Physa 

 eat anything living, although small snails and other animals 

 have been caught in its slime. The struggle of the animal 



