XIII ARACHNIDA 183 



of extra, very small, fine threads which are given out by 

 the spools for this purpose, but which are quite distinct 

 from the " spigot threads " which form the line. 



Other details of the uses of special spigots or spools are 

 given below in describing the web-formation and the egg- 

 cocoon.^ The action of the spinnerets can be readily seen 

 when the spider is making her web. 



Just below the spinnerets is the «««.?, situated on a little 

 process which projects forwards (Fig. 116). 



There is no segmentation of the abdomen to be seen, 

 though a few bands of darker coloration occur just above the 



S^ \ 'Is 



Fig. 117. — Diagrammatic longitudinal section through the body of a young 



Epeira ( 9 ). 

 <ij Anus ; s, spinneret ; sg and sg\ silk glands ; sjj, spiracle ; t, tracheae ; o, ovary ; Is, 



lung-sac ; Ji, heart ; ss, stomach ; d, diverticulum of stomach ; e, eyes ; j>, poison 



gland ; o, opening of gland on mandible ; m,, mouth. 



spinnerets. These have, however, nothing to do with any 

 true segmentation. 



Lung-books ^^ front of the darker patch on the abdomen can 



and be seen the two transverse slits, which lead into the 



Tracheae, respiratory organs, known as the "lung-books." 



(The slit-like spiracles, or " stigmata," are shown in Fig. 1 1 6 as 



the lower line on each of the two light areas below the 



abdomen.) 



The special kind of respiratory organs known as "lung- 

 books " occur only in air-breathing Arachnids. 



Each of the stigmata opens into a small cavity extending 

 forward. From the front wall of this cavity there project 



^ See also paper by C. Warburton in the Q. J. Mior. Sci. for April 1890. 



