322 WILLIAM MORTON BARROWS. 



center of the web usually hesitated, turning first toward one, then 

 toward the other, finally orienting to one and attacking this by 



itself. 



3. Response in the Dark. 



In order to test the ability to respond in the dark the vibrator 

 was set up late in the afternoon, the straw touching one of the 

 radial strands of a web which was built in the frame of a window. 

 The window was shaded on the outside by a heavy thicket. At 

 9:30 P.M. the room was so dark that a person standing inside 

 could discern the outline of the window with the utmost difficulty. 

 A flash of light from a pocket electric lamp showed that the female 

 occupying the web was at the center of her web. The vibrator 

 switch was closed and at the end of about four seconds the electric 

 flash light showed the spider biting the vibrator straw in the 

 same manner as that shown in Fig. 3. This experiment indicates 

 that unless these spiders use rays of light which our eyes do not 

 perceive, sight plays no essential part in the orientation to and 

 the ensnaring of the prey. 



4. The Distribution of Vibrations through the Web. 

 The distribution of vibrations as they travel across the web is 

 of some theoretical interest. The following method for recording 

 these vibrations was used with considerable success. A spider 

 in its web was placed before the camera and made to respond to 

 the vibrator repeatedly until it would respond no more. A 

 photograph (Fig. 5) of 15 seconds' exposure was then made while 

 the vibrator was in motion. The web was somewhat torn by 

 the spider before it ceased to respond, but the photograph reveals 

 by the thickening of the lines the distribution and amplitude of 

 the vibrations in all parts of the web. The amplitude of the 

 vibrations decreases rapidly from the periphery toward the 

 center. The radial strand connected with the vibrator shows 

 the greatest lateral displacement while the strands on either side 

 of this show less and less disturbance as the distance away from 

 the vibrator increases. A slight thickening of the spiral strands 

 in a direction at right angles to the direction of the primary vi- 

 bration can be noted on the segments directly across the center 

 from the vibrator. The center of the web seems to be the part 



