138 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



are established. Their tents are woven against the upper surfaces of the 

 round rocks and their snares fill the openings. In a number of these, 

 made by adults (August), the proportion of full round orbs was much 

 greater than sectoral orbs. I am not able to account for this remarkable 

 difference, as nothing in the site gave a clue. It would almost seem that 

 the species is in a state of transition from the one habit to the other ; 

 the habit of weaving a sectoral orb being now in the ascendant, but the 

 power to spin full orbicular snares remaining intact and sometimes be- 

 coming dominant. 



The wedge like open space always occupies the upper semicircle of the 



snare, but has no fixed posi- 

 tion therein. I conceived the 



idea that the orien- 

 Orienta- tation of the en 



tion of i v 



s , sector and traplme 



might have some 

 special relation to the econ- 

 omy of the spider, or even to 

 its structure. But, after mak- 

 ing an immense number of 

 notes and sketches of webs, I 

 concluded that the matter is 

 largely dependent upon the 

 convenience of a site for pitch- 

 ing the shelter tent. Some- 

 times the sector opens directly 

 upward as in the typical snare 

 at Fig. 123, sometimes to the 

 left, or again to the right. 

 Much the greater number of 



FIG. 123. Triaranea's snare, o, orb ; m, the maze ; g, guy lines Openings noted by me Were On 

 supporting orb ; d, den or tent ; f, free radius ; c, central. Q 



ing the object), and next to that the favorite position was at the middle. 

 The sectoral opening usually occupied about the space of one-eighth of the 

 surface of the orb. I have measured sectors covering respectively about one- 

 fifth, one-sixth, one-eighth, one-tenth, and one-fourteenth of the same. Or, 

 the proportions may be yet better understood by these measurements. Let 

 ab (Fig. 124) represent the diameter of several orbs and cd the width of 

 the sector at the circumference. In No. 1, ab = two and a half inches, 

 cd six-eighths inch, three-tenths the orb space; No. 2 (Fig. 124), ab = 

 two and a half inches, cd = one inch, two-fifths the orb space ; No. 3, ab = 

 two and a half inches, cd one-half inch, one-fifth; No. 4 (Fig. 125), ab = 

 two inches, cd = three-eighths inch, over one-fifth ; No. 5, ab = two inches, 

 cd= three-eighths inch, one-fifth orb space; No. 6, ab=two inches, cd 



