2l8 'Journal of Comparative Neurology and Psychology. 



Experiment II. Case I- — Ten first-stage larvae, five hour's old, 

 were placed in a glass tube 40 cm. long, and this was laid on the 

 table at right angles to the plane of the window and parallel to the 

 light rays entering through a narrow slit in the screen. All of the 

 larvae at once oriented themselves at the window end of the tube. 

 Next, blue, green, and yellow glass plates were placed successively 

 over the end of the tube next the window, leaving the opposite 

 end clear, but none of these changed the definiteness of the posi- 

 tive reaction. When, however, an orange glass was used, the larvae 

 paused midway in the tube, at the border line of the orange light, 

 and in their final orientation were scattered between this region 

 and the orange end of the tube. When a red glass was superim- 

 posed, all the larvae took a position at the border line of the red 

 and the clear glass, this region representing the junction of the 

 areas of strong and weak illumination. 



Experiment 12. Case i — In this experiment the glass bottomed 

 box A was set up over the light-shaft with the colored glass plates 

 arranged in the order, red, orange, green, blue, as described on 

 p. 207. The box was filled to a depth of one inch with water 

 and first-stage larvae, twenty-four hours old, were introduced. 

 Five minutes was allowed for the larvae to become acquainted 

 with the new environment. Records of four tests then made 

 showed that while thirty-eight larvae gathered in the blue area, 

 only one was found in the red, one in the orange, and none in the 

 green. Changing the order of the glasses in no way changed the 

 results. This apparently demonstrates that there is a definite 

 tendency on the part of these larvae to orient themselves over the 

 glass plates which admit the brightest light; and that the precise 

 order of the plates makes no difference in orientation. 



Case 2 — In this instance the order of the glass plates was red, 

 orange, green, blue. The same larvae used in the above tests were 

 employed, but the conditions of the experiment were changed. 

 The window in the end of the box corresponding to the red glass 

 was uncovered and the diffuse light from the room was allowed 

 to stream through the box longitudinally. The object of this was 

 to discover whether the larvae which had previously given so defi- 

 nitely the positive photopathic reaction, could be induced to enter 

 the region of diminished light intensity (at the red end of the box). 

 In other words, whether the phototactic reaction could be made 

 to overcome the photopathic. Between each of the successive 



