COMPOSITE SNAKES AND SECTORAL ORBS. 



133 



The Orb 

 Described 



The orb of Labyrinthea is a delicate and beautiful structure. It is not 

 large in size, usually measuring six or seven inches at the longitudinal axis 

 and five or six at the lateral. The largest web I ever saw was 

 twelve inches in diameter. 1 Within this space are disposed a 

 large number of finely spun radii and spirals, the former some- 

 times numbering as high as seventy-five, the latter exceeding eighty. The 

 spirals, as is common in orbwebs, are more numerous below than above the 

 hub, but this difference is very marked in the web of Labyrinthea, some- 

 times being as great as three to one, and even six or seven to one. 2 The 

 spirals in the lower part of the orb are not complete circles, but are looped 



in, the lines terminating at the sides. 



in full orbwebs, and is habitual in 



The diminished number of spirals 



due to a peculiar feature of the snare, 



bination of characteristics 

 Construe- read alluded tQ Thig feft 



tion L/en- " . , , . ., 



tral Space 11011 of lhe spiders domicile 



essary that the 

 the snare in order to give 

 its outer surface ; and, sec 

 direction of the trapline 

 opening than would oth 

 is illustrated at Fig. 117, 

 of the orb from behind 

 view to the connection 

 hub, and its relations to 

 seen that the unbeaded 

 zone are cut off above, 

 space somewhat like the 

 orb. This opening is 



This feature is sometimes seen 

 sectoral orbs. (See Fig. 121.) 

 at the top of the orb is in part 

 which at least suggests that com- 

 of full orb and sectoral orb al- 

 ture results, first, from the posi- 

 behind the orb, making it nec- 

 trapline should penetrate 

 the spider admission to 

 ond, from the slanting 

 which compels a larger 

 erwise be required. This 

 which shows the centre 

 and above with a special 

 of the trapline with the 

 the spirals. 3 It will be 

 spirals of the notched 

 leaving a triangular open 

 free radius of a sectoral 

 larger or less according 



to circumstances; it may be increased by the trapline impinging upon 

 the spiral space, thus leaving but a few continuous spirals at the top of 

 the orb. The spider when seeking prey runs through this opening, under- 

 neath the overspun arch of spiral lines, to the outer face of the orb upon 

 which the insects are ensnared. It returns along the same path to the 

 tent with the captured insect. 



1 The following measurements in inches show ordinary sizes : 7 inches long by 6 wide ; 

 6x5; 6x6;9x7; 6 x 4i ; 12x12. 



2 The following counts will illustrate this : No. 1, radii, 55 ; spirals, 31 above, 82 below. 

 No. 2, spirals, 8 above, 55 below, 47 at the sides. No. 3, radii, 75; spirals, 80. 



3 Measurements of Fig. 117, orb 9 in. long by 7 wide; hub f in. long, f wide; centre 

 of hub 2} in. (about one-third the length of the orb) from the top margin of the orb. 

 The hub is meshed, oval, narrowed at the top. The notched spirals fill the Free space, 

 three being close to the hub, the others widening as they wind. Traplines about 2 

 in. long. 



