REACTIONS OF ORB-WEAVING SPIDER TO VIBRATIONS OF WEB. 325 



the vibration of the whole leg or whole body. Hinged sensitive 

 hairs uniformly scattered over the body might answer this pur- 

 pose. It seems most likely, everything considered, that the 

 particular sense organs used are on the tarsi of each leg and come 

 in contact with the web. It is difficult to conceive that an animal 

 whose feet are not extremely sensitive could travel on or manipu- 

 late the delicate strands of these orb-webs. 



IV. DISCUSSION AND SUMMARY. 



It is maintained in this paper as in a previous one (Barrows, '07) 

 that an animal exhibits a "tropism" or better a taxis, "when 

 under the influence of [chemical] stimuli acting unilaterally they 

 move toward or away from the source of the stimulus" (Verw r orn, 

 '99, p. 249). It has been shown above that Epeira sclopetaria 

 orients in its web and moves toward the source of a vibratory 

 mechanical stimulus when this is of an appropriate rate and 

 amplitude. Thus this method of response to a vibratory stimulus 

 identifies the reaction as a positive taxis. The term tonotaxis 

 would naturally be used in this connection, but since tonotaxis 

 has been used in another way it seems advisable that the terms 

 positive vibrotaxis should be applied if a short descriptive term 

 is desired. 



The foregoing may be summarized as follows: 



1. Epeira sclopetaria, an orb-weaving spider, starting from the 

 center of its web is able to orient, charge and seize flies which 

 strike and are detained in the web. This process is carried out 

 with extreme rapidity. 



2. With the aid of a mechanical vibrator it is possible to show 

 that the stimulus is vibratory, the spider orienting to and 

 attacking the vibrator even in the dark. 



3. The response can be analyzed into, (a the orientation, 

 (b) the forward response, and (c) the attack on the vibrating 

 object. The response is in essence a positive vibrotaxis. 



4. The vibrations are transmitted through the web in all 

 directions from the vibrating point but the intensity (amplitude) 

 decreases toward the center of the web and on either side. The 

 lines of equal intensity of the vibration form roughly a series of 

 circles the centers of which are at the vibrating point. 



