46. ARACHNOIDEA, 



CASE it is Studded all over with minute globules, which do not imme- 

 diately dry up, and remain viscid to the touch; and it is by 

 means of this sort of bird-lime that its prey is detained and 

 attached, until the spider has time to spring upon it from its 

 ambush. This viscid gum is not distributed over all parts of 

 the web alike. That would interfere with the spider's own 

 freedom of motion. It therefore forms the main radii or stays of 

 the web of threads free from this gum, and on these it nms freely, 

 while the prey, ignorant of these safe bridges or gangways, flounders 

 hopelessly in the net itself It is probable that the glue that 

 forms the viscid globules is supphed by different tubes from the 

 kind that hardens, and that the tubes of both kinds are inter- 

 mingled, so that as the threads are forced out they come in con- 

 tact with this viscid secretion, which runs together in globules 

 through the elasticity of the thread, drawing it out more than it 

 can bear without division. 



The silken threads of which the webs are thus made are used 

 by many species belonging to various genera for other purposes 

 besides catching their prey— one is to enable them to take aerial 

 excursions. Some have thought that the creatures could dart out 

 their threads from their spinnerets to such a distance as to use 

 them like rafts to float on in the atmosphere. That they do float 

 through the air so supported is true— but not by darting out the 

 threads. Experiments have proved that it is the rarefied air of 

 fine weather that wafts the thread away from the spider, and that 

 it only avails itself of their support to take the journey. Such 

 threads, or webs, broken from their moorings, compose the filmy 

 webs named gossamer, which, on being brought into contact by 

 the breath of gentle airs, adhere together until, by continual 

 additions, they accumulate into irregular white flakes of surprising 



quantity. 



Efl"orts have been made to turn the spinning powers of spiders 

 and the silk they secrete to practical purposes, but without much 

 success. In the beginning of the last century an ingenious 



