122 SPIDEKS : THEIR STRUCTURE AND HABITS. 



adjacent radii are left open to prevent the spider from being 

 caught in her own net. The E. i?idmata, so called from the 

 oblique position of its web, bites away the tuft which united all 

 the radii at the centre, and takes her station near the circular 

 opening thus formed. She extemporises a line of retreat wherever 

 required, lowering herself to the ground by a thread fastened to 

 the innermost spiral, and re-ascending by it when the' coast 

 is clear. 



Our admiration of these webs, so true in all their proportions, 

 is increased when we consider that they are executed entirely by 

 the sense of touch. The eyes of spiders are so convex that they 

 can discern objects only at very small distances ; it is, therefore, 

 unlikely that they can be of much service in guiding the move- 

 ments of organs so remote, and so much out of the line of sight, 

 as are the hind feet and the spinnerets. 



It is moreover a well-ascertained fact that webs spun by the 

 Epeiridce. in the dark betray no irregularity of plan, nor imperfec- 

 tions of workmanship. An instance came under my own obser- 

 vation last autumn. 



It is an interesting question how these different kinds of 

 thread are produced from the same spinning apparatus. We have 

 noticed in the web of the Epciridce three distinct threads, — one 

 differing from both the others in being adhesive and highly elastic. 

 Now, examination proves that the former property, the stickiness, 

 is not inherent in the thread but in the globules alone; for when 

 these are carefully removed the thread is left perfectly unadhesive, 

 while yet retaining its elasticity. These, therefore, must be the 

 product of a different kind of secretion from that which produces 

 the threads ; for the latter possess indeed ductility in a high 

 degree, but are unadhesive, while with the globules the case is 

 exactly the reverse. We have therefore to account for four, if not 

 five, distinct products, viz. — three kinds of thread, the viscid 

 globules, and the Hquid gum or solder, used by all Retiary 

 spiders in fixing their threads. 



The supply of viscid material in the spinning apparatus of the 

 Epeiridce must be considerable ; for according to the calculations 

 of Mr. Blackwall, the number of globules in a Geometric Spider's 

 web of average dimensions, is not less than 87,000, while in a 

 large web of 14 or 16 inches diameter, they must amount to near 

 upon 120,000. 



To assist our inquiries the microscope furnishes us with the 

 following data respecting the spinning-organs : — 



(i) — In the Retiary Spiders the spinning tubes are far more 

 numerous than in the Hunting Spiders ; and this is pre-eminently 

 the case with the Epeiridce^ the total number exceeding 1,000 in a 



