338 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 
up the various lines of the snare, so that all the radii, particularly, are 
held in a tense condition. 
This tension of the trapline and radial lines makes the whole web an 
efficient telegraphic instrument for conveying to the spider in her den or 
domicile any vibration caused by insects entangled upon the snare. When 
by such telegraphy the capture of an insect is communicated to the sen- 
sitive feet of the spider, she immediately rushes along her trapline to the 
hub, and from that point to her prey. Thus, in the typical Orbweaver’s 
snare, the trapline serves the two purposes—first, of communicating to 
the proprietor the presence of entangled insects; and, second, of affording 
a gangway to the net and back again to the tent. In short, the incidental 
dragline appropriated to the uses of a gangway, in Epeira strix, is here 
specialized into a trail and a telegraph. 
As far as I can positively affirm, no other than these two purposes 
are served by the trapline in these species. However, it is the habit of 
spiders who thus use this specialized instru- 
ment to frequently pull upon it, increasing the 
: tension by drawing it towards them- 
Jerking selves and then letting it go again, 
the Trap- ‘ : ee 
ice making a series of rapid jerks. I 
have never been able to observe that 
this motion had any purpose or effect to in- 
crease the entanglement of an insect, and haye 
always regarded it simply as a means of deter- 
mining the presence, weight, and energy of the 
iia gaae de aeares wept epg victim, and thus estimating the degree of call- 
at her hub, to show the radiiclus) tion necessary in approaching it. If the insect 
ene IE ae be quiescent, as often occurs, the pulling and 
sudden relaxing of the trapline is quite sure to set it in motion again. 
It might, perhaps, be observed in this connection that even when the 
spider is hanging on guard at the centre of her orb, she spins a series of 
deltated lines, the apex of which is grasped by several claws of 
the legs, and the opposite ends of which are attached to the 
radii in such a way as to cause a direct communication between all parts 
of the orb and the sensitive feet within which these lines are thus con- 
verged. Examples of this are especially observable in the various species 
of Acrosoma. Fig, 329 shows the manner in which Acrosoma rugosa, when 
hanging upon the open hub of her snare, thus gathers converging radii 
into her claws. A like habit in the cases of Acrosoma mitrata and spinea 
is illustrated by Figs. 112 and 113, page 127. In the same manner that 
the trapline is jerked by nest building Epeiras, in order to tighten it and 
test the presence of insects, this series of footlines is also frequently jerked, 
and apparently for the same purpose. 
While I cannot record observations which justify me in asserting that 
Footlines. 
