BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 309 



The glass dishes and the fragments were all carefully cleaned 

 before using. The glass fragments were powdered in a glass 

 mortar and then washed. The culture fluid was carefully filtered, 

 and the amebas were transferred through several washes of 

 filtered culture solution. 



A fragment of glass was placed near a raptorial ameba 125. 

 As the main pseudopod moved forward it forked, the left limb 

 moving toward the glass 126, 127. The right pseudopod moved 

 on for a short distance, then turned sharply toward the left and 

 moved into contact with the glass 128-130. The right limb 

 was then withdrawn and the ameba moved off through the left. 

 The glass seems to have been sensed at a distance of about 

 forty microns 128, 129 perhaps at sixty microns 126. A 

 few minutes later a new fragment of glass was laid in the ameba's 

 path 133. The ameba at first turned to the right, but a little 

 later a pseudopod was sent out on the left which moved almost 

 into contact with the glass, but was then withdrawn 136-139. 

 The main pseudopod broke up into three pseudopods, one of 

 which moved a short distance toward the glass and was then 

 retracted. The pseudopod on the right, which with the left 

 one already mentioned formed a pair of opposite pseudopods, 

 then became the main pseudopod through which the ameba 

 moved away. There is no doubt that the ameba received 

 stimuli proceeding from the glass; the formation of the pair of 

 opposite pseudopods shows it, as does also the retraction of the 

 left pseudopod before the glass was reached. The same piece 

 of glass was again laid in the ameba's path 141. The ameba 

 moved toward it a short distance, then turned slightly to the 

 right and moved on 142-144. When the tip of the main 

 pseudopod was even with the glass fragment, a side pseudopod 

 was sent out toward the glass and into contact with it 145, 146. 

 The tip of the main pseudopod also turned over toward the glass 

 and then moved into contact with it. Both pseudopods were 

 then withdrawn while the ameba moved off through a pseudopod 

 on the right. The ameba sensed the glass in Fig. 142 at a distance 

 of over sixty microns. The same piece of glass was then shifted 

 149. The ameba moved directly forward to within about 

 forty microns of the glass, when the tip of the pseudopod spread 



