BIOLOGICAL MISCELLANY. 67 



of lier luib, aud is in the following manner : The body is bowed or 

 arched a little more than is usual when in that position, and then is set 

 in motion in such wise as to cause the web to move back and 

 th B d ^'^^'^^^ swinging upon its foundation lines. The motion is at first 

 slow, and is rapidly increased until communicated to the whole 

 web, which is oscillated at times so violently that the form of the spider 

 becomes indistinct. This motion is continued for several minutes, the 

 period varying in length. Mr. Muybridge, distinguished for his observa- 

 tion upon the motions of animals, informed me that he once watched a 

 female Argiope cophinaria in continuous oscillation on her snare for a 

 half hour. 



The oscillation of the orbs bj^ Argiope appears to be accomplished by 

 lifting the abdomen up and down, or rather back and forth, from the web, 

 and the alternate slackening and drawing taut of the line which connects 

 the spinnerets with the central silken shield. At the same time the legs 

 are alternately bent together and stretched out, thus drawing the orb in 

 and repelling it. These movements of the spider of course put tlie orb in 

 oscillation, and when rapidly repeated it moves back and forward with 

 great rapidity. 



Among Lineweavers this habit takes the forni^ of a rapid whirling of 



the body within the snare. The species most addicted to this habit is our 



common long legged cellar spider, Pholcus phalangioides. This 



Whirhng creature hangs upon its snare of large loosely netted cross lines 



, with its back downwards. Its feet, which are stretched upward 



from the bodj^, by reason of the great length of the legs clasp 



these lines well together. Then begins a circular motion of the body. 



This at first is slow, but is rapidly increased until the body whirls around 



in circles so rapidly that it can scarcely be distinguished from the whole 



mass of agitated lines, legs, and body, which resembles a revolving cone. 



The manner in which the motion is produced is probably the same in 

 both tribes here mentioned, but the nature of the Orbweaver's web is such 

 that the motion is limited by the upper and lower foundation lines within 

 which it is set, and is so compounded as to compel the orb to a lateral or 

 pendulum like movement ; that is, a movement perpendicular to the plane 

 of the orb. In the case of Pholcus, however, the web of right lines per- 

 mits the body to revolve in cii'cles which are parallel to the plane of the 

 horizon. 



This habit is doubtless protective, and jarobably serves to confuse attack- 

 ing Hymenoptera, birds, and other enemies, and thus avert thoir aim or 

 drive them from the position by the unwonted agitation of the 



TTcoc of 



th H h't ^'^^- ^^^ ^^^ origin and chief purpose are probably connected 



with the taking of prey. The swaying of the web must aid to 



entangle more completely a victim which strikes it, since it stimulates the 



captive to increase its struggles aud thus more effectively to fasten itself to 



