16 AMEBOID MOVEMENT 



The ingestion of a large food mass produces usually a marked 

 change in streaming. A more or less spherical form is assumed, 

 and if the food mass be a live organism such as a large ciliate, 

 the ameba frequently remains quiet for a considerable interval. 

 If a large amount of food is eaten, as for example a dozen or two 

 colpidia, the ameba may suspend concerted streaming for an hour 

 or more. During this time small pseudopods are projected here 

 and there, but there is no locomotion. But if an ameba eats large 

 masses of carmine, there is usually no pause following ingestion, 

 and the same thing is true when the ameba is induced to eat bits 

 of glass and other indigestible substances. It follows therefore 

 that the interrupted streaming of the endoplasm due to feeding 

 is not caused by the act of ingestion as such, but rather by the 

 onset and continuance of the normal digestive processes on a 

 large scale. These reactions are again strikingly similar to what 

 is observed in many vertebrates, in which a more or less definite 

 body sense, whose sense organs are in the splanchnic region, is 

 supposed to be involved ; but what the explanation of similar be- 

 havior in ameba is, is not at all clear. 



Another factor of great importance in endoplasmic streaming 

 is the nucleus. It was observed by Hofer ('90) that amebas lack- 

 ing nuclei did not move in a coordinated manner. Stole ('10) 

 however records a number of observations in which characteristic 

 movement was observed in enucleate amebas ten or more days 

 after the enucleate ameba had been cut off from a normal ameba. 

 Hofer's amebas died after nine or ten days, while Stoic's remained 

 alive, some of them for over thirty days. Recently Willis (16) 

 confirmed Hofer's findings, but does not discuss Stoic's results. 



The cutting of an ameba into two pieces, one with and the other 

 without a nucleus, is a very simple operation. It is also very easy 

 to observe that within an hour or so the enucleate ameba does not 

 move normally, and that there is no concerted endoplasmic stream- 

 ing while the nucleate ameba seems to behave normally. But 

 Stoic's contention that enucleate amebas move characteristically 

 (1. c., p. 159, 1 60, 167) is not necessarily contradicted by these 

 observations, for Stoic's observations refer to amebas that lived 

 much longer than the enucleate amebas of Hofer and of Willis. 

 Even if an enucleate ameba is able to recover, after many days, 



