OHAPTEE XIII. 



ENGINEERING SKILL OF SPIDERS. 



I. 



IT is a generally received opinion, even among well informed natural- 

 ists, and is certainly a fixed popular tradition, that Orbweaving spiders 



construct a web that is perfectly true in its geometric arrange- 



Imperfect ment. This has highly redounded to the praise of the little 



Teomet- weaverj particularly as she may spin by the sense of touch with- 



out the aid of sight. 1 It seems a pity to destroy any notion 

 ment. that mav throw around despised Arachiie a greater measure of 



respect in the popular mind, in which her standing is, as a rule, 

 anything but favorable. However, in the interests of truth it must be said 

 that concerning this point the popular opinion is only true in a general 

 sense. There is much irregularity in the execution of many geometric 

 webs. 



The radii are not laid out with absolute mathematical accuracy, but 

 are separated from each other by distances varying considerably. If, for 

 example, one carries the eye around the circumference of this large orb, 

 he will find here two radii terminating upon their marginal foundation 

 lines at points half an inch apart, and there two others three-fourths of 

 an inch apart, and in yet another place two others separated by one and 

 a half inches. It is true that all orbs are not laid out as irregularly as 

 this from whose measurements I have quoted, but more or less irregularity 

 will be found on almost every web, particularly upon those spun by adult 

 spiders. Again, the radii will be found blending with one another at 

 various points instead of converging regularly upon a central point; and 

 more or less departures of a like kind from mathematical accuracy char- 

 acterize the spiral concentrics. However that may be, the actual facts in 

 the case are sufficiently striking, and the general regularity of plan ;m<l 



the frequent close approach to geometric accuracy in special orbs 

 Symme- are remarkable enough without resorting to exaggerations. In 

 E , . , fact, it may well be doubted that absolute regularity, in the 

 ' sense of symmetry, would be the most desirable for the uses of 

 a web. The departures from mathematical accuracy may mark, and I 

 have reason to believe do mark, a higher measure of utility, and 



1 See Wood's "Homes without Hands," page 321. 



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