1916] Wilson: On the Life-History of a Soil Amoeba 265 



The flagellate occurs regularly in the cultures, but there are few 

 in comparison with the number of amoebas. For example, on a cover- 

 glass which has so many amoebas on it that there is very little space 

 not covered by them, there will be from one to five, occasionally more, 

 flagellates in a field of a %-ineh objective. If the medium next to the 

 upper and lower surfaces of the culture is examined about the same 

 number will be found. 



The first flagellates found in the pure mixed cultures of amoeba and 

 bacteria M'ith M'hieh this work is concerned were found in a hollow- 

 slide preparation which had been made by sealing an amoeba film with 

 vaseline over the cell filled with distilled water. It was examined after 

 sixteen hours and there were a few flagellates among the amoebas. 

 showing that flagellates may be produced entirely cut ofl: from the air. 

 Since then they have been produced in material from old cultures and 

 in those from individuals recently obtained from the soil. Once they 

 were found on an agar plate, but this medium was very little used 

 and so their behavior on it cannot be discussed. 



To turn a whole film of amoebas into flagellates, it is only necessary 

 to add a few drops of distilled water to the cover-slip containing them. 

 It has been found by experiment that more of the amoebas enflagellate 

 in this than when sterile medium is used. The cover-slip is then left 

 film side up exposed to the air of the room, which is better than that of 

 a moist chamber. A preparation which has turned into amoebas over- 

 night may be stimulated to enflagellate in the morning by the addition 

 of more distilled water. IMost of the amoebas of a preparation will be 

 transformed to flagellates in three hours. 



A little over an hour after the preparation is made (the time varies 

 from one hour to one hour and fifteen minutes), contracting amoebas 

 will be found at different places over the cover. These will be found 

 to be more or less free from the substratum and to be moving the free 

 portion through a rather large extent of space by this jerky movement. 

 Short pseudopodia are sent out and drawn in almost continuously. The 

 amoebas twist and turn, getting nearer all of the time to the rouuded- 

 up condition. When they reach a thick, .short, pyriform shape, they 

 swim away with the narrow flagellated end anterior (pi. 22, fig. 97). 



The flagellate stage is not of long duration. If undisturbed, a 

 preparation in which the first flagellates appeared at eleven o'clock in 

 the morning, was practically free of all flagellates by nine o'clock in 

 the evening, and only two or three, even fewer, could be found in a 

 low-power field the next morning. These may have been some that 



