134 



ARACHNIDA. 



however, appear to have neither pores nor papillse. On ex- 

 amining the spinnerets more minutely, it will be found that 

 each is surrounded T\dth several series of minute bristles, like 

 points, about one thousand to each spinneret. From each 

 of these points or spinnerules is discharged a thread, so that 

 it may be easily conceived of what an immense number of 

 distinct threads the apparently simple thread of the spider 

 consists. The first object which the spider has to accom- 

 plish is to attach her thread to some substance, as the com- 

 mencement of a ground-work for her future operations. In 

 doing this, it appears that she extends her spinnerets as 

 widely as possible, presses them against the object to which 

 it is intended the thread should be attached, and then dis- 

 charges a thread from each of the spinnerules; the spinnerets 

 are then withdrawn, and the threads, by degrees, are united 

 into a single cord ; the insect uses her hind legs as a reel to 

 draw the threads out of her body. It appears, however, that 

 the threads are of different kinds ; for in the webs of the 

 geometric spiders, those threads which are arranged in circles 

 are composed of more \dscid materials than the radii, the 

 former being evidently intended for secm*ing the prey of the 

 spider, and the latter serving merely as its frame-work, and 

 destitute of gluten. This viscidity is produced by an im- 

 mense number of globules of viscid matter, arranged at 

 visible distances along the elastic spiral lines of the net, and 

 which are so fluid that they run together the moment they 

 are brought into contact. Mr. Blackwall has given a calcu- 

 lation of the number of these viscid globules in the web of 

 one of the EpeircB of a moderate size, and which conveys 

 some idea of the elaborate operations of the geometric 

 spiders. The mean distance between the radii in one of 

 these nets is about seve^-tenths of an inch; there are twenty 

 viscid globules on one-tenth, of an inch, so that there are 

 7 X 20 = 140 globules in a single line between two contigu- 

 ous radii seven-tenths of an inch apart : this product, multi- 



