182 



INTRODUCTION TO ZOOLOGY 



hanging from a thread, it is always with these opposable 

 claws that the spider grips. 



.pjjg The much-swollen abdomen bears underneath, 



Abdomen near its tip, the spinning glands or " spinnerets." 



and its These consist of three pairs of short, very 



pinnere s. j^Q^jjjg processes. The second pair in Epeira is 



hidden below the others when not in use, consequently only 



two pairs show in Fig. 116; these 



two are each two-jointed, but the 



median inner pair has only one 



joint. 



At the tip of each process are 

 small projections of different sizes, 

 on which are the openings of the 

 silk-spinning glands of the abdomen. 

 As many as 600 glands open on 

 separate little projections on the 

 thiee pairs of spinnerets ; from each 

 of these a gummy fluid can be 

 emitted which, as it dries in the 

 air, forms a fine silken thread. 

 Certain of the projections are larger 

 than the others, and are known as 

 the "spigots" to distinguish them 

 from the much smaller and more 

 numerous processes, known as the 

 "spools." There is one spigot on each 

 of the first pair of spinnerets, three 

 on each of the second, and five on each of the third pair. The 

 spigots and spools have their own special functions, the former 

 giving out stronger, coarser silk threads than the latter ; the 

 silk used in making the lines of the web is usually emitted from 

 the spigots of the first pair of spinnerets alone, though some- 

 times a spigot on each of the median spinnerets adds an 

 additional strengthening strand ; the web threads are there- 

 fore double or sometimes fourfold, the strands adhering to 

 each other along their whole length, but being quite easily 

 separable. The popular idea that these threads consist of 

 many strands woven into one by the spider is erroneous ; it 

 arose probably from the fact that each of the main threads is 

 tethered, as it were, to its point of attachment by a number 



Pig. 116. — Epeira diademata. 



Ventral view showing .iaws, pedi- 

 palps, legs, two pairs of spin- 

 nerets, and anal papilla. 



