The Internal Anatomy of Spiders 



in some spiders there are as many as twelve. They are large, 

 long glands, more or less cylindrical in outline (Fig. 143, and Fig. 

 175). The glands consist of an epithelium invested by a peri- 

 toneal membrane. The epithelium is continued into the duct, 

 which also has a chitinous intima. 

 Each gland opens through a spigot 

 (Fig. 172 c). In the usual condi- 

 tion, when there are four of these 

 glands, the spigots are located one 

 on the inner side of each of the 

 fore and middle spinnerets. The 

 ampullate glands occur in all species 

 examined. They are termed am- 

 pullate because each is furnished with an ampulla or 

 sac-like dilation. 



The drag-line and the dry threads of webs are 

 made of silk from the ampullate glands. The fact 

 that the drag-line is composed of only two or four 

 strands and that it comes from these glands was dis- 

 covered by Warburton ('90). 



The source of the elastic element of the viscid 

 thread of the orb-weaving spiders has not been 

 determined. It appears to come from the centre of 

 the group of spinnerets; as it consists of two strands 

 of considerable size, it is evidently spun from two 

 spigots. As the drag-line of orb-weavers usually 

 consists of two strands, I infer that in these spiders 

 two of the ampullate glands have been so modified 

 that they produce elastic silk. Wilder ('66) demon- 

 strated that the yellow silk of Nephila, which is the Fig I7S- 

 viscid silk, is spun from the fore spinnerets. an 



/ he cylindrical glands. — I hese glands are com- gland 

 monly present in female spiders; but are wanting in 

 the Dysderidae and in the Attidae. There are usually six of 

 them; but sometimes there are many. In males there is a 

 smaller, number or they are wanting. In the usual case, where 

 there are six cylindrical glands, one opens on the outside of 

 each middle spinneret, and two open on the inside of each hind 

 spinneret. Each opens by a spigot similar to the spigots of the 

 ampullate glands, but with a wider opening (Fig. 172, d). 



173 



