XIII ARACHNIDA 185 



This line is then strengthened, for the spider walks along 

 it and fixes another thread to it as she goes. 



By repeating this process, several strong boundary threads 

 are laid down, usually forming an irregular, four or five-sided 

 figure. These first threads may frequently stretch right 

 across a window frame a yard or more in width ; in fact, 

 cases are recorded where they were three times this length. 



The spider next starts on the construction of 

 of the^elf ^^ ^^ itself, fixing a thread near the centre of 

 the top boundary line, and dropping with it, or 

 carrying it round, to the centre of the opposite boundary, and 

 fixing it there. To the middle of this first diagonal, other 

 threads are fixed and carried out as spokes in all directions, 

 until there are sufficient radiating threads to support the 

 spiral, now to be formed. The centre or "hub" is strengthened 

 each time a thread- is fixed there ; the framework also is 

 frequently strengthened by additional threads, binding it to 

 fresh supports, so that it becomes very irregular in shape 

 (Plate I.). 



Then, starting from the centre, the spider first 

 Thread ^^'''^^ there a little irregular platform, and, from 

 just beyond this, she starts a spiral line which 

 is fixed to each spoke as it crosses it. The first line winds 

 in a wide spiral of several turns, and is only a temporary 

 scaffolding, to give foothold, whilst the spider finally lays 

 down the very viscid spiral which constitutes the effective 

 snare, in which insects are caught. All the previously formed 

 threads dry in the air, so that they are not in the least sticky ; 

 the viscid substance now used for the snare is given out from 

 special spigots on the last pair of spinnerets. 



The permanent spiral is begun at the circumference of 

 the web, and is laid down with great care, each piece of 

 thread being slightly stretched as it is fixed to the spoke it is 

 crossing, and then suddenly released. It springs into its final 

 position, and as it does so, the viscid fluid, which until now 

 has covered it uniforndy, is shaken into a series of little 

 globules that hang on the thread, and can be seen distinctly 

 with a lens, though invisible to the naked eye. 



As she lays down the viscid thread, the spider moves 

 along the first non-viscid spiral, biting each piece away after 

 she has made use of it. 



