686 GEOFFREY TiAPAGB 



a conclusion with wliich I am entirely in ugreement. The 

 behaviour of Amoeba proteus in its capture of large 

 Ciliata like Paranioeciuni and Col])idium in cultures strikingly 

 supports the same view (cf. also Schaeffer, 23). 



Penard (21, p. 700) has descril)ed another instance of the 

 chasing of one amoeba by another wliich ended in the fusion of 

 the two, and Leidy (18) has described and figured what is 

 undoubtedly the successful capture and digestion of an 

 Amoeba verrucosa by Amoeba proteus. This 

 latter case is particularly interesting, since Leidy says that the 

 A. verrucosa assumed, in the body of its captor, 'the 

 appearance of a large sphere, still retaining its contractile 

 vacuole unchanged '. Later on the ' victim had become 

 pyriform and striate, and was tlien included in a large water 

 vacuole. Still later the body of the A. verrucosa appeared 

 to have become broken up into five spherical, granular balls. . . .' 

 Leidy was unable to follow the ultimate fate of these ' granular 

 balls ', but he supposed that they were digested. A comparison 

 of Leidy "s figures with those illustrating this paper leaves no 

 doubt that he was dealing with an isolated instance of a process 

 which was occurring on a larger scale in my cultures. 



The fact, however, that Leidy 's is the only one of these 

 cases in which anything resembling actual digestion was seen, 

 and the fact that I have only in one instance (cf. below) seen 

 in my cultures doubtful evidence of digestion of the spheres, 

 suggest that the amoebae only rarely are able to digest other 

 amoebae which they may capture. Further, it seems probable 

 that amoebae only rarely even attempt to capture other 

 amoebae, and usually fail to retain these when they are active, 

 however frequently they may succeed in ingesting them when 

 they are sluggish or resting in a rounded-off condition. 



The case in which the doubtful evidence, referred to above, 

 of digestion of a sphere was seen, was that of a sphere wliich 

 was spherical when it was ingested, but which did not remain 

 so. It underwent distinct form changes while it was still inside 

 its captor. PL 29, figs. 8 and 10, represent other ingested 

 spheres, drawn from stained preparations, which had assumed 

 an irregular form while inside their captors. In the case just 



