THE GENESIS OF SNARES. 



345 



From 

 Sheet to 

 Dome. 



nearly approaches, in the habitual form of its snare, that form which, as 

 I have shown, incidentally results from the long use of Theridium's web 

 of intersecting lines. 



The step is not a large one by which we may conceive the snare just 

 described to be transformed into that of the dome shaped web of Linyphia 

 marginata, or the bowl sluiped web of Linyphia communis. It 

 only needs, in the former case, a little more downward pressure 

 ujion the cords at the edges, and in the latter a little more 

 pressure upon the marginal cords upward, to complete the proc- 

 ess. (Fig. 33.5.) We may now pass from Lineweavers to Tubeweavers. A 

 glance at the snare of Agalena noevia, for examj^le, as represented in 

 Fig. 215, page 217, and Fig. 336, will show how close is the resemblance 

 between it and the snares of Linyphia already described. Agalena has a 

 sheeted web of open spinningwork, or of close, irregular meshwork, as one 

 may choose to put it, whose weft becomes 

 much thickened in course of time by fre- 

 quent overlaj'ing. It also has the crossed 

 lines extending upward, for the most part, 

 but often downward also, representing the 

 original rude intersecting lines of our sup- 

 posed primitive snare. This retitelarian fea- 

 ture of the web is a most important factor 

 in the daily capture of prey, by signaling 

 their presence to the waiting proj^rietor ; 

 by arresting and trapping them so that they 

 fall upon the sheeted premises beneath ; and 

 by actually entangling them. 



This most highly organized of all the F'g-SSB. sheeted web and tube of Agalena 

 . . , - , ncevia, woven on a hedge. 



Tubeweavnig species has therefore substan- 

 tially a Lineweaver's snare. To this structure is added the tube, which, 

 in point of fact, is not the snare, but the nesting place. I have already 

 shown, in the chapter on Nesting Habits (Chapter XVIL), the manner in 

 which this feature of the" snare may have been gradually developed by 

 the natural action of the spider. In point of fact, the tube is the typical 

 nest of all species, and is naturally formed by the movements of the spider 

 within a limited space, spinning out as it moves the silken material which 

 it secretes. 



Theridium, and still more habitually and definitely Linyphia, will form 

 a little tube like structure by the mere gravity of the body as it hangs 

 upon its snare in this manner: The eight legs reach upward. 

 From forming what may be called the sectional outline of a tube cut 

 „ , horizontally. The weight of the spider, aided by the violent agi- 



tation of its snare when struck by an insect, pulls down these 

 eight points in such a way that a little conical or dome like tent is formed 



