1913] Gee: Behavior of Leeches 217 



Examination of the position of these collections usually re- 

 veals that they are located in the least lighted portions of the 

 dish. In the center of many of them can be seen a mass of 

 debris, which, coming in contact with the body of the first one 

 or two leeches forming the group, causes a cessation of move- 

 ment. The others composing the collection were directed to the 

 same locality by the influence of the light rays and came to rest 

 one by one until a considerable group was established. As 

 already suggested, the animals show a very strongly positive 

 thigmotaxis. Undoubtedly, optimum light conditions and thig- 

 motaetic responses are the chief factors operative in the formation 

 of collections. 



This tendency to formation of collections is much more mani- 

 fest in Glossiphonia stagnalis than in Dina. Even under stones 

 in their native environment large groups are to be found. When 

 the groups are formed in dishes in the laboratory they occur 

 principally in the angles of the dish. Often as many as fifty 

 to a hundred individuals are to be found composing a single 

 collection. ' 



2. Food op Leeches 



Moquin-Tandon (1846) has observed: "Les Nephelis man- 

 gent des Limnes et des Planorbes; elles s'emparent aussi des 

 Planaires, des Monocles, des petites larves aquatiques et des 

 animalcules infusiores. II parait d'apres la structure de leur 

 bouche, qu 'elles ne se eontentent pas de sucer ces animaux, mais 

 qu 'elles en avalent des portions considerables." Of HerpodeUa 

 otoculata, a form related to Dina microstoma, Harding (1910) 

 says : ' ' This and the succeeding species devour small oligochaetes 

 such as Tubifex. planarians. and probably a variety of other 

 soft-bodied animals." Bristol (1898) in his work on the meta- 

 merism of Nephelis records the fact that he "fed chopped fresh- 

 water clams. ... I have kept individuals for over a year in 

 normal condition, and have raised many young under these 

 conditions." lijima (1882) in his paper on the embryology of 

 Nephelis says: "If well fed with fish meat or larvae of mos- 

 quitos, Nephelis will lay eggs in abundance." 



