]916] Wilson: On the Life-History of a Soil Amoeba 243 



found that the equatorial plate came from the karyosome, while 

 Chatton (1910) and Wasielewsky and Hersehfeld (1910) described it 

 as coming from the peripheral chromatin. Alexeieff (1911) says it 

 comes from both. 



A flagellate stage in the life-cycle of an amoeba has been found by 

 a number of workers. Among these Schaudinn (1896), in Paramoeia 

 eilhardi, described this stage and found division occurring in it, as does 

 Craig (1910, 1911) in his Paramoeha hominis. Sehardinger (1899) 

 in his paper on " Entwieklungskreis einer Amoeba lobosa" describes 

 various experiments on the tlagellated stage which he calls Amoeba 

 gruberi. His material came from diarrhea stools and the medium used 

 was hay- or straw-agar. He found that amoebas in a hanging drop al 

 25°-30° C began turning into flagellates after seventy minutes, at 

 which time the pseudopodia were shoi-ter. In one hour and fifteen or 

 twenty minutes the flagella were formed on about ninety per cent of the 

 individuals. He found that he could turn the flagellates thus obtained 

 back into amoebas when he chose. There were four methods which he 

 found would accomplish this: (1) increase of temperature to about 

 34° C, (2) intense lighting, (3) hindrance of free movement, and (4) 

 the addition of fresh food. 



Wasielewsky and Hirschfeld (1910) described a biflagellate stage 

 in an amoeba from hay infusion and one from an infusion from tan- 

 bark. Whitmore (1911) in Trimastigamoeba philippincnsis found 

 individuals with three and sometimes two or four flagella, some of 

 which he showed with basal granules and rhizoplast. Alexeieff (1912 a) 

 described the flageUate stage of Amoeba punctata Dangeard. Wherry 

 (1913) working on the same species as that of this paper found this 

 stage. He produced it by diluting the medium and exposing it to 

 atmospheric oxygen. 



There are numerous other accounts of Amoeba, but in no ease has 

 the life-history of any one species been described. This discrepancy 

 was pointed out by Profe.ssor C. A. Kofoid. to whom I am indebted 

 for direction and much kindly assistance. 



The purpose, then, of this work is to contribute as much as possible 

 to our knowledge of the life-history of a single species. In pursuance 

 of this, daily observations have been made for most of the time for the 

 past two years. 



II. MATERIAL AND METHOD 



The material was obtained from undisturbed alluvial soil along 

 Strawberrv Creek in the glade by the Faculty Club, on the campus of 



