THE GENESIS OF SNARES. 



349 



rinthea, and Thaddeus (Fig. 341), and, indeed, by all the nest making 

 species, such as the Furrow, Insular, and Shamrock spiders. This feature 

 of their spinningwork is readily ac- 

 counted for, and appears most closely 

 to connect that tribe with the other 

 tribes of the spinning fauna. It is, 



however, far more difficult 

 Origin of explain the origin of 

 Orbwebs. fe 



such a remarkable habit as 



the construction of an orbicular snare 

 of that geometric character with which 

 the reader is now familiar. We ap- 

 proach it, however, from the direction 

 of the Tubeweaving genera, as Dic- 

 tyna and Clubiona. The fact has 

 heretofore been alluded to, that they 

 are provided with special organs, the 

 cribellum and calamistrum, for the 

 exudation and preparation of a floc- 

 culent thread out of which their trap- 

 ping lines are spun. These threads 

 are placed upon lines composed of or- 

 dinary spinningwork, which usually 

 diverge with more or less regularity from some common point. The manner 



of placing them is well illus- 

 trated by Fig. 342, where the 

 curled thread is seen spread 

 along its supporting lines, and 

 passed from one line to anoth- 

 er, and so back and forth 

 throughout the snare. 



This would seem to be a 

 most natural movement. It is 

 precisely the one which, as we 

 have explained (see Fig. 95, 

 Chapter VI.), is re- 

 Dictyna's sorte( j to ^y Argiope 



Curled i i 



g . , cophmana and Argi- 



Thread. P e argyraspis when 

 they form the zigzag 

 band which adorns and charac- 

 terizes their round web. It is 

 naturally produced by the striding movement of a spider between two 

 lines, swinging her abdomen backward and forward as she moves. In 



FIG. 343. The snare of the Wall loving Dictyna, 

 woven on a Philadelphia city wall. 



FIG. 344. Orb like snare of Dictyna philoteichus, woven 

 against a wall. 



