72 The Structure atid Habits of Spiders. 



SUJ&. The principal difficulties are the space 

 needed for keeping each spider by herself, and 

 the amount of labor needed to pro\"ide them 

 with living insects for food, and to draw out 

 the silk, which would make it too expensive to 

 use. 



CURLED WEBS. 



There is a family of spiders called by Black- 

 wall Cinijlonida, see p. 17, which, besides the 



'MWmS^ 



i'ig- 33- 



usual plain thread, make a peculiar kind of 

 their own. They have in front of the spin- 

 nerets. Fig. 33, an additional spinning-organ 

 called the cribellum, a, a. It 15 covered with 



