66 ASA A. SCHAEFFER. 



forward until it came nearly into contact with the dark beam 

 when a slender pseudopod moved into the dark area, and another, 

 indicating a tendency to negative behavior, moved to the right 

 498. But when the ameba came into contact with the globulin 

 the pseudopod on the right was withdrawn and then the globulin 

 was ingested, the ameba quieting down over the dark spot. The 

 experiments with this ameba show that the dark beam may be 

 sensed at a distance of at least 150 microns, and that the globulin 

 may be sensed as well apparently when lying on a dark spot as 

 when illuminated. 



A dark spot with a fragment of carbon lying on it was placed 

 to the right of an ameba 503. There was no definite response. 

 The ameba turned toward the right and moved toward the test 

 objects in a more or less uncertain manner 504, 505. A pseu- 

 dopod was then sent out on the left 506. After it had attained 

 to considerable size it was withdrawn and the ameba moved off 

 through a pseudopod thrown out on the right 508. The ameba 

 was shifted with the carbon-dark spot lying on the right 509. 

 As the ameba moved forward it turned toward the right 510 a 

 small pseudopod being formed, as frequently happens, on the 

 convex side, but a pseudopod was presently thrown out on the 

 left 513 through which the ameba moved away. To show 

 that it was the dark spot and not the carbon which produced 

 the negative behavior, the results of the next experiment are 

 appended 514. The ameba moved directly into contact with 

 and on over the carbon without any sign of a negative reaction. 

 A grain of globulin lying in a dark beam was then placed at some 

 distance to the right of the ameba 520. An accidental jar 

 displaced the globulin so that it lay near the anterior edge of the 

 dark spot. The ameba changed its direction of motion and 

 moved straight toward the globulin and the dark beam 521. 

 (It may reasonably be doubted whether the ameba sensed the 

 globulin at this distance.) The globulin was then moved to the 

 further side of the dark beam 522. The ameba kept on moving 

 forward for some distance, then its behavior became somewhat 

 uncertain. The ameba moved slightly to the left 524. A 

 pseudopod which was thrown out on the right 525 became 

 later the main pseudopod. The ameba now moved directly 



