46 ASA A. SCHAEFFER. 



plasmodia and pelomyxas, the first to be recorded appear to be 

 those of Verworn. ('89). He projected white light and various 

 spectral colors of various intensities perpendicularly through the 

 microscope slide, and observed no change of reaction as the ameba 

 moved from one intensity to the other, or from one color to the 

 other. With the experiment similarly staged, Davenport ('97) 

 came to the same conclusions as Verworn. Amebas moved from 

 a field of very weak light into one of very strong light, apparently 

 without change of behavior, even when the change of intensity 

 was sharp and abrupt. But Davenport showed that when a 

 light beam is projected horizontally against an ameba, the ameba 

 orients so as to flow away from the source of light. Harrington 

 and Learning ('oo) showed that intense white, violet, or blue 

 light, flashed on a moving ameba, arrested its movement mo- 

 mentarily; but red light was without any decisive effect. Mast 

 ('10), experimenting under conditions similar to those under 

 which Verworn and Davenport worked, confirmed Davenport's 

 findings when horizontal beams of light are thrown against an 

 ameba, and also concluded from his experiments that when an 

 ameba finds a perpendicular beam of intense light in its path, it 

 avoids the light in many cases. Mast also confirmed the general 

 conclusions of Harrington and Learning. 



None of these investigators observed any but negative be- 

 havior, though Mast presumably looked for positive responses, 

 for he says "I was unable to obtain positive reactions in Stentor 

 c&ruleus, Amceba, and fly larvse" ('n, p. 270). The reason 

 Mast failed to get positive responses was because the beams of 

 light which he used were too large and the light was too intense. 

 And further his apparatus was perhaps defective. He says: 

 "The beam of light was produced by focusing a limited area of a 

 luminous Welsbach mantle on the slide by means of the mirror 

 and an Abbe condenser" ('n, p. 78). If he used an ordinary 

 microscope mirror, as he seems to have, a very faint subsidiary 

 beam as well as the very intense primary beam, was projected 

 through the slide. The one is produced, of course, by the front 

 surface of the glass, and is very readily overlooked; the other is 

 produced by the surface of the silvering. Since the subsidiary 

 image shows only on one or two sides of the main image, if square, 



