BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 307 



the carbon were retracted as the ameba moved away through 

 the pseudopod which had been forming on the opposite side. 

 Some time later another grain of carbon was laid in the ameba's 

 path 226. Two pseudopods were formed on the right, through 

 the anterior one of which the ameba moved away, disturbed 

 probably by the commotion caused by placing the carbon in the 

 ameba's path. The same piece of carbon was again laid ahead 

 of the ameba 230. The ameba at first turned away from the 

 carbon 231, 232 but later turned toward it 233. A pseudo- 

 pod was then sent out toward the carbon until it came into 

 contact with the carbon 235-237, then it was retracted and the 

 ameba moved off, directly away from the carbon 239. A few 

 minutes later a new piece of carbon was laid in the ameba's 

 path some distance ahead 240. The ameba then broke up 

 into several pseudopods, but finally moved ahead a short distance 

 through the main pseudopod. A pseudopod was then sent out 

 on the right, which moved into contact with the test substance 

 and apparently ingested it in a typical food cup. The ameba 

 kept on moving forward, and two minutes after apparent inges- 

 tion the carbon was left behind. (The curved leader line 

 straightened out, is the measure of the distance the ameba 

 moved away in a straight course from the carbon grain.) The 

 same piece of carbon was again laid ahead of the ameba 264. 

 As the ameba moved forward it turned to the left and away from 

 the carbon, but as it passed by the carbon two pseudopods were 

 sent out toward it 267. The posterior one came into contact 

 with the carbon, moved on over it, and spread out; but no 

 attempt at ingestion was made. The pseudopod forked and the 

 ameba moved along the left prong. A new piece of carbon was 

 then laid to the left of the ameba's path 271. As the ameba 

 moved forward, a pair of side pseudopods which were begun 

 simultaneously on opposite sides 274 continued to enlarge 

 until the one on the left began to flow over the carbon. Then 

 the pseudopod on the right was retracted and the ameba flowed 

 away through the pseudopod extended over the carbon. 



To summarize the behavior toward carbon : The most striking 

 feature of the behavior toward pure carbon is that the ameba can 

 sense this substance at a distance of at least forty microns. It 



