BY W. J. RAINBOW. 533 



It will be conceded, therefore, from the facts here stated, that 

 the bridge-lines of webs are influenced by the direction of air- 

 currents. At the same time I am free to admit that in the case 

 of webs consti'ucted within a narrow space, and where the Ijridge- 

 lines are short, spiders do sometimes carry the line to the opposite 

 point of attachment. 



In 1881 Dr. McCook, at the close of an interesti^ig address 

 delivered before the Academy of Natural Sciences, Philadelphia, 

 said : — " While this use of air-currents is certainly placed beyond 

 doubt, it is as certainly not the only mode of laying foundation- 

 lines, and is dependent very much upon the site chosen, the 

 condition of the wind, the abundance of prey, etc. Webs built 

 in large open spaces are perhaps alwaj's laid out by bridge-lines 

 [i.e , lines carried by air-currents. — W.J.R.]. In more contracted 

 sites, the frame lines are generally carried around, and often a 

 foundation is the result of both methods."* 



Some time ago it was my good fortune to discover what may 

 certainly be considered an extraordinary web. This peculiar 

 snare was stretched between three large shrubs, the situations of 

 which described a triangle (.".), and was what may be denominated, 

 for want of a better term, a "double" web. The main body of 

 the mesh consisted of the typical orb, with the customary outer 

 lines or guys, but at the back, and running down the centre, the 

 spider had placed a semi-orb. I spent a long time in looking for 

 the interesting architect, but without success, and it is quite 

 possible it may have fallen a pre}' to some insectivorous bird. 

 Other orbitular snares are occasionally met with, having cords 

 attached to the centre or " hub," drawn taut, and firmly secured 

 to a branch or trunk of a tree, thus causing the snare to be 

 sharply depressed, the object being, doubtless, to strengthen it 

 against the wind. 



Snare-fabricating spiders form two great tribes : the Orbitu- 

 lar icb and Retitelarice; the webs of the former are more or less 

 geometrical, orb-like, in most instances erected in a vertical 

 position, though sometimes oblique, and in some instances hori- 



* Proo. Acad. Nat. Sci. Philadelphia, 1881, p. 435. 

 35 



