SPIDERS. 45 



CA|E respects, the general form and structure of spiders is that of 

 insects. There is one important peculiarity however, viz., the 

 spinnerets by which they spin the webs, which are the most dis- 

 tinguishing and remarkable feature of the family. 



The spinnerets are placed at the tail end of the abdomen, and 

 consist of two, three, or four pairs, according to the kind of spider. 

 They vary also in form, being round, cylindrical, or conical, and 

 their tips and under surface are pierced with numerous minute 

 holes, like the rose of a watering-pot, through which the liquid 

 that becomes the thread is pumped out. It is a liquid glue, and 

 each jet of it comes out as a thread of infinitesimal tenuity; and 

 the whole multitude of fine threads is compacted together into a 

 single line of extreme fineness, but great comparative strength. 

 That this is so may be easily proved by taking any of the 

 large spinning spiders, say one of the diadem spiders (Epeira 

 diademata), and after pressing its abdomen against a leaf or other 

 substance so as to attach the threads to its surface— the same 

 preliminary step that the spider adopts in spinning— drawing it 

 gradually to a small distance. It can then be plainly perceived 

 that the proper thread of the spider is formed of four smaller 

 threads, and these again of threads so fine and numerous that 

 there cannot be fewer than a thousand issue from each spinner. 



tThe glue is a viscid fluid, which is secreted by glands in the 

 abdomen, and is conducted to the spinneret orifices by tubes ; 

 when exposed to the air — and it is very probably for the purpose 

 of exposing it all instantaneously that it is made to issue in such 

 fine threads— it hardens into a most elastic silk, so elastic that its 

 apparent rapid lengthening or shortening has given rise to the 

 erroneous belief that the spider can retract it into its abdomen. 

 This it cannot do; after it has once come out and hardened, 

 there it remains. But there must either be more than one kind 

 of glue or silk secreted, or else the one kind must be capable 

 of modification by the animal in its passage out, for while the 

 spider's thread itself becomes immediately hard and unadhesive. 



