Nets of Geometric Spiders. 185 



this procedure she takes her station and watches for her prey. In this 

 account I recognize the proceedings of one only among several species of 

 geometric Spiders with which I am acquainted. As far as my own obser- 

 vations extend, it never, hke the last species, converts a radius into a Hne 

 of communication with its retreat; and when it occupies the aperture in 

 the centre of its snare, a thread from its spinners is generally connected 

 with the innermost circumvolution of the unadhesive spiral line, by means 

 of which it quickly lowers itself to the ground when suddenly disturbed. 

 But there are other species which rarely, if ever, leave a vacant interval 

 round that portion of the unadhesive spiral line allowed to remain near 

 the centre of the net ; neither do they form an opening at the centre, 

 which almost invariably is left entire. 



The reason why the viscid spiral line is not continued to the centre of 

 the net is obvious, for by this arrangement the Spider is enabled to super- 

 intend her toils without incurring the risk of being entangled in them. 

 The species referred to by Messrs. Kirby and Spence as always leaving a 

 vacant interval round the smallest first spun circles that are nearest the 

 centre of her net, produces fewer of these small circles than any other 

 Spider that has fallen under my notice ; consequently, if the viscid line 

 were prolonged till it made a near approximation to them, the unadhesive 

 lines about the centre would be too closely circumscribed, and the Spider 

 would be subjected to great inconvenience. 



Hitherto I have supposed the Spider to form her snare in places evi- 

 dently easy of access to her ; but it is not unusual to see nets fixed to 

 objects between which it is quite impossible that a communication can 

 have been established by any process alluded to above ; between distant 

 plants, for example, growing in water. " Here then," as the authors of 

 the Introduction to Entomology observe, " a difficulty occurs. How 

 " does the Spider contrive to extend her main line, which is often many 

 " feet in length, across inaccessible openings of this description ?" To 

 this curious fact my attention has long been directed, and I have thoroughly 

 satisfied myself, by observation and experiment, that in such instances 

 Spiders invariably avail themselves of currents of air, by which their lines 

 are sometimes conveyed to a surprising distance. 



If the geometric Spiders be placed on twigs set upright in glazed 

 earthen-ware vessels with perpendicular sides, containing a sufficient 



