ON THE FEEDING HABITS OF AMEBA 545 



stances are poured into the vacuole before it is quite surrounded 

 by protoplasm. 



Most of the cases of feeding described in this paper were accom- 

 plished through food cups that were formed against the glass 

 surface of the object holder. But food cups may readily be form- 

 ed free, out of contact with any solid object excepting the food 

 object. In a case where a small flagellate became entangled in 

 the upper surface of the ectoplasm a circular ridge of protoplasm 

 appeared with the flagellate in the center. The ridge was ex- 

 tended upwards until well above the flagellate, when it gradually 

 closed in upon the flagellate and a considerable quantity of water. 

 It is possible also to produce such a free food cup experimentally, 

 by stimulating a part of the ameba mechanically with a very fine 

 glass needle. 



Size of food cups 



The size of food cups varies very greatly among the different 

 types of amebas. Among the raptorial forms the maximum 

 limit is determined only by the amount of protoplasm in the 

 ameba. In fact, in numerous instances, a whole ameba may be 

 engaged in the starting of a food cup which, to complete, of the 

 size projected, would take the protoplasm of several amebas. 

 The minimum size of a food cup among raptorial amebas is just 

 large enough to take in a small diatom. 



With the granular amebas the size of the food cups is less vari- 

 able. They very seldom involve more than three-fourths of the 

 protoplasm, and even then the walls of the cup are thicker than 

 in the raptorial form. It is difficult to say what the minimum 

 size of a food cup is. A small organism like the flagellate chilo- 

 monas is ingested in a food cup nearly always large enough to 

 accommodate easily the ciliate coleps. But particles of isolated 

 proteins are frequently ingested in food cups scarcely larger than 

 the particle itself. 



The size of the food cups in all amebas roughly corresponds to 

 the size of the stimulating object. Especially is this the case if 

 only moving organisms, or if the various kinds of lifeless food, 



