COMPOSITE SNAKES AND SECTORAL ORBS. 



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

 large in size, usuall}' 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. ^ AVithin this s^jace are disposed a 



The Orb 

 Described 



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.^ 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- ^,^^. ^^^^^^^^^ ^^ rpj^i^ f^^ 



tion Cen- . „ , . , , , ... 



tral Space tion of the spider s 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 



hul>, and its relations to 



seen that the unbeaded 



zone are cut off above, 



space somewhat like the 



orb. This opening is 



Fifi. 117. Centre of Labyrinthea's 

 orb, showing arched opening. 



Tliis 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 com])cls a larger 



erwise be required. This 



which shows the centre 



and above with a special 



of the trapline with the 



the spirals.* 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 overspunarch 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. 



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

 6x5; 0x6; 9x7; 6 x 4J ; 12 x 12. 



- The following counts will illustrate this : No. 1, radii, 5.5 ; spirals, 31 above, S2 below. 

 No. 2, spirals, S 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 ^ in. long, f wide; centre 

 of hub 2k 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 ' 2J 

 in. long. 



