the dragline is derived from one pair, and the elastic strands of 

 the viscid line from the other pair. In Amaurohius there are 

 three pairs of ampullate glands, and in the viscid thread, as will 

 be shown later, there are two pairs of supporting strands. If 

 one pair of ampullate glands produce the dragline of these 

 spiders, there remain two pairs of ampullate glands, from which 

 the two pairs of supporting strands of the viscid thread may be 

 derived. 



Let us pass now to a brief study of the more or less fluid 

 viscid silk. 



The simplest form of this silk is what may be termed the 

 swathing film of the Theridiidœ. This silk is emitted from two 

 or four spigots, one or two, as the case may be, on each of the 

 hind spinnerets. These spigots are the outlets of the lobed 

 glands, which have been found only in this family. The swathing 

 film is flung by these spiders over their prey by means of a 

 comb of hairs on the tarsus of the hind legs, the presence of 

 the lobed glands and the tarsal comb being distinctive charac- 

 teristics of this family. 



Except in the Theridiidœ, those spiders that secrete viscid 

 silk place it upon a supporting thread or band of threads. The 

 simplest form of this type of silk is the viscid spiral line in the 

 webs of the Argiopidœ. The structure of this viscid line is well 

 shown by Fig. 5, which is a photomicrograph of a short section 

 of thread. 



This thread is composed of two elements — the elastic sup- 

 porting thread which consists of two strands, already discussed, 

 and a series of fluid, viscid drops. It is believed that this fluid 

 viscid silk is secreted by the aggregate glands, as these glands 

 are found only in those spiders that produce this type of thread. 

 I have watched the making of this viscid thread, and have seen 

 that at first the viscid silk forms a continuous coating on the 

 supporting strands : this was while the thread was being pulled 

 from the spinnerets by one of the legs. During this time it was 

 greatly stretched, being several times as long as the space between 

 the two radii upon which it was to be placed ; after the thread 

 was fastened to the second radius, it was allowed to contract 

 by the withdrawal of the leg, and as soon as the tension was 

 relaxed the coating of viscid silk collected in drops. 



