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 open 
tion of ; 
Ranken sector and trapline 
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. 
A sai Pry Much the greater number of 
Fic. 128. 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. the right side of the web (fac- 
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 ed the width of 
the sector at the circumference. In No. 1, ab = two and a half inches, 
ed = six-eighths inch, three-tenths the orb space; No. 2 (Fig. 124), ab= 
two and a half inches, ed = 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 = 
