32O WILLIAM MORTON BARROWS. 



orients instantly and advances along the nearest radius to the 

 straw, seizes the straw with its mandibles and may spread web 

 on the straw with the hind pair of feet (Fig. 3). This reaction 

 is carried out in essentially this manner no matter where the 

 straw may strike the web. 



The orientation is so rapidly executed and is followed so closely 

 by the forward locomotion that it is difficult to separate the two 

 parts of the response. If, however, the vibrator is set in motion 

 for a fraction of a second only the orienting is accomplished but 

 the forward locomotion toward the vibrator does not follow. 

 A second vibration while the spider is oriented calls forth the 

 forward response and an attack on the vibrator (Fig. 3). The 

 photograph reproduced in Fig. 2 shows such an orientation. If 

 the first vibratory stimulus is not too long or is not followed by a 

 second stimulus the spider usually returns to the resting position 

 at the end of a few seconds. Some individuals, however, follow 

 the orienting response by an interesting series of activities. 

 The fore feet are placed on neighboring radii, drawn toward the 

 animal's body and released suddenly. This release sets the web 

 vibrating parallel to the spider's longitudinal axis. The spider 

 then turns one space to the right or left and repeats the process 

 until she has oriented through a complete circle and set every 

 pair of radii in motion. The use of this activity is seen if there 

 happens to be a captured fly or a piece of dirt in the web. When 

 the two radii which pass on either side of the object are set vibrat- 

 ing the object is also set in motion but its motion is not of the same 

 rate as that of the rest of the web and it sets up an echo or return 

 vibration. To this the spider responds. A dead fly may be 

 rediscovered in this way or a piece of dirt may be located and 

 removed. 



Responses to different frequencies show considerable variations 

 and it is not possible to predict that a certain individual will 

 respond in a definite way to a given stimulus. This variation in 

 response ranges from instantaneous orientation and forward 

 locomotion to a slow orientation and slow approach toward 

 the vibrating point or it may happen that no sign will be given 

 that the stimulus has been perceived. Roughly speaking a large 

 spider responds most quickly to a vibration of considerable am- 



