and the dry threads of webs are composed of only two or four 

 strands, each of which issues from the type of spinning tube now 

 known as a spigot. 



The most general use of silk by spiders is for the protection 

 of their eggs ; and it is not improbable that this was the primi- 

 tive use of this substance by these animals. But having acquired 

 the ability to produce silk, it was natural that it should be put 

 to other than its original use, for it is a substance that is available 

 for many different purposes. 



In the present state of our knowledge, an attempt to trace 

 the steps by which the several kinds of silk glands, producing 

 silk fitted for widely diñerent purposes, have been evolved from 

 the primitive type of silk gland, would be largely hypothetical, 

 and I will not presume to undertake it. But I confidently 

 believe that such a study would throw much light on the phylo- 

 geny of the families of the Araneida. 



The different kinds of silk produced by spiders can be grouped 

 into three classes : first, silk consisting of very many, extremely 

 slender strands ; second, silk consisting of a small number of 

 comparatively large strands ; and third, a more or less fluid, 

 viscid silk. 



The first of these three classes of silk, that consisting of 

 very many, extremely slender strands, is produced by the pyri- 

 form and the aciniform glands, which are present in large num- 

 bers, and which open through the small type of spinning tubes. 

 These are the spinning tubes that have been most often observed 

 and described. 



From the pyriform glands, which open through the small 

 spinning tubes of the fore spinnerets, are spun the attachment 

 disks, by means of which the larger threads are fastened to 

 various objects. Each attachment disk (PI. TIT, fig. i) consists of 

 many exceedingly fine loops, and is made by applying the fore 

 spinnerets to the object upon which the disk is to be made, 

 and by alternately spreading apart and bringing together these 

 spinnerets the looped threads are drawn from the small spinning 

 tubes. This operation was described by Apstein and can be 

 easily observed by enclosing a living spider in a bottle, and 

 watching it with a lens as it fastens its dragline to the side of 

 the bottle. 



