THE BEHAVIOR OF AMCEBA 



13 



ingest them. One or two concrete cases will illustrate the behavior of 

 Amoeba when presented with the problem of obtaining such an object 

 as food. 



A spherical Euglena cyst lay in the path of an advancing Amoeba 

 proteus. The latter came against the cyst and pushed it ahead a short 

 distance. The cyst did not cling to the protoplasm, but rolled away 

 as soon as it was touched, and this rolling away continued as long as the 

 animal moved forward. Now that part of the Amceba that was imme- 

 diately behind the cyst stopped moving, so that the cyst was no longer 

 pushed forward. At the saine time a pseudopodium was sent out on 

 each side of the cyst (Fig. 18), so that the latter was enclosed in a Httle 

 bay. Meanwhile, a thin sheet of protoplasm passed from the upper 

 surface of the Amoeba 

 over the cyst (Fig. 

 18, 2). The two lat- 

 eral pseudopodia be- 

 came bent together at 

 their free ends; the 

 cyst was thus held so 

 that it could not roll 

 away. The pseudo- 

 podia and the over- 

 lying sheet of proto- 

 plasm fused at their 

 free ends, so that the 



cyst was completely enclosed, together with a quantity of water, 

 was then carried away by the animal. 



Amoeba does not always succeed in obtaining its food so easily as 

 in the case described. Often the cyst rolls away so lightly that the 

 animal fails to grasp and enclose it. In such a case Amoeba may con- 

 tinue its efforts a long time. 



Thus, in a case observed by the author, an Amceba proteus was mov- 

 ing toward a Euglena cyst (Fig. 19). When the anterior edge of the 

 Amoeba came in contact with it, the cyst rolled forward a httle and 

 slipped to the left. The Amoeba followed. When it reached the cyst 

 again, the latter was again pushed forward and to the left. The Amoeba 

 continued to follow. This process was continued till the two had trav- 

 ersed about one-fourth the circumference of a circle. Then (at 3) the 

 cyst when pushed forward rolled to the left, quite out of contact with 

 the animal. The latter then continued straight forward, with broad 

 anterior edge, in a direction which would have taken it away from the 

 food. But a small pseudopodium on the left side came in contact with 



Fig. 18. - 



- Amoeba ingesting a Euglena cyst, 

 sive stages in the process. 



I, 2, 3, 4, succes- 



It 



