THE MOVEMENTS AND REACTIONS OF AMOEBA. 22^ 



This theory is a most attractive one, and seems a priori probable.* 

 It is conceivable that there may be, or may have been, organisms where 

 it is applicable throughout. But an objective study of the behavior of 

 Amoeba shows that it gives by no means an adequate explanation of 

 food-taking in this animal. As I have shown in the descriptive por- 

 tion, in Amwba proteus and A. angulata the food in most cases is far 

 from adhering to the protoplasm ; on the contrary, it rolls away when 

 the Amoeba comes in contact with it, and it is often only as a result of 

 long-continued effort that the animal succeeds in ingesting it. The 

 first act in ingestion consists in sending out pseudopodia on each side of 

 the mass to overcome the mechanical difficulty resulting from the fact 

 that the body does not adhere to the protoplasm, but tends to roll away. 



Further, a quantity of water is usually, or frequently, taken in with 

 the food, and the latter floats about in a cavity after it is ingested, show- 

 ing no tendency to adhere to the protoplasm (see Leidy, 1879, numer- 

 ous figures of food vacuoles, etc., and Le Dantec, 1894). A similar 

 condition of affairs is shown in the account of the feeding of one 

 Amoeba on another, given on page 201 of the present paper. Here the 

 prey does not adhere to the protoplasm of its captor, but moves about 

 within the latter and escapes repeatedly. 



Thus, in these species, the taking of food and the choice of food can- 

 not be explained by the adherence of the protoplasm to the food sub- 

 stance, for the lack of such adherence is strikingly evident. 



Rhumbler's studies of food taking were made chiefly on Amwba 

 vcrrucosa. In this species and its close relatives there is much more 

 tendency for foreign objects to cling to the surface than in the other 

 species. But this adhesiveness applies to other objects as well as to 

 food. It is of special aid, as we have seen, in tracing surface move- 

 ments (p. 140). Particles of soot and various other indifferent bodies 

 stick to the surface, rendering its movements apparent. Not all such 

 adhering bodies are taken into the interior, so that the ingestion 

 involves an additional reaction, and is not fully accounted for by the 

 adhesion even in these species. 



Rhumbler has given an ingenious physical analysis of the rolling up 

 and taking in of filaments of Oscillaria by Amoeba verrucosa, and has 

 illustrated the process as he conceives it to occur by a very striking 

 experiment (1898, p. 230). A chloroform drop brought in contact 

 with the middle of a filament of shellac rolls the filament together and 

 encloses it. Rhumbler conceives the forces at work in rolling up the 

 filament to be essentially the same in the chloroform drop and in the 

 Amoeba. In both cases, according to Rhumbler, the surface tension of 



* See Jennings, 1902, where I adopted this view before having investigated for 

 myself the behavior of Amoeba. 



