silk from either the pyriform or aciniform glands. The retreat 

 of Ayanca thaddeus (PL III, fig. 4) is a good illustration of this. 



The most familiar illustration of the second class of silk, 

 that consisting of a few strands of comparatively large size, 

 is the dragline spun by most spiders wherever they go. This 

 ordinarily consists of two strands, and is spun from the ampullate 

 glands, as was first determined by Warburton. Fig. i repre- 

 sents an attachment disk with the dragline leading from it. 

 This line is the thread that forms the principal part of the webs 

 of spiders. In orb-webs, the foundation lines and the radii are 

 made of it. 



Another kind of silk consisting of a few strands of consider- 

 able size is the foundation thread of the viscid spiral. This 

 resembles the dragline in consisting of two strands, but differs, 

 as is well known, by its great elasticity. It is evident that this 

 elastic line is spun from two spigots. And by a process of 

 elimination we can infer that it is spun by one of the two pairs 

 of ampullate glands possessed by the orb-weavers. 



The threads of which egg sacs are composed also consist of 

 a small number of comparatively large strands ; but the number 

 of the strands is greater than in the kinds of silk produced by 

 the ampullate glands, being six or more in all that I have ex- 

 amined. It has been well established that this silk is produced 

 by the cylindrical glands. 



Of silk that is evidently spun from spigots there remains to 

 be mentioned the supporting strands of the viscid threads spun 

 by the cribellate spiders. Of the source of these nothing definite 

 has been determined by direct observation. But I venture 

 to suggest that these strands are spun from the ampullate glands. 

 In Amaurobius, which was studied by Apstein, and which can be 

 taken as a type of the Cribellate, the only glands that open 

 by spigots are the ampullate and the cylindrical. Hence these 

 large threads must be spun from one of these sets of glands. 

 As the well-known function of cylindrical glands is the pro- 

 duction of the threads of which the egg sac is made, there remain 

 only the ampullate glands from which these strands could be 

 derived. 



I have suggested that with the typical orb-weavers, the 

 ArgiofidcB, where there are only two pairs of ampullate glands, 



