XIV. INTRODUCTION. 



indigenous spiders traces may be seen of transverse folds in the 

 cuticle towards the hinder extremity. Probably the transverse 

 curved, or angular lines above noticed, and which give to the 

 hinder part of the abdomen of so large a majority of spiders, 

 its distinctive pattern, are the lingering indications of obsolete 

 folds. The traces of folds (as well as the corneous plates in 

 ZipMstius) in all probability point to the once segmented structure 

 of the abdomen, and give us a clue to the origin of the distinctive 

 pattern just mentioned. 



At the extreme point of the hinder part is a single small 

 nipple-like prominence (pi. i., fig. 10, f) ; in this is contained the 

 anal orifice ; and it was, doubtless, once the terminal segment 

 of the segmented form of the abdomen. 

 Spinners. 



Immediately below the anal prominence, is a more or less- 

 closely compacted group of other nipple-like organs (pi. i., fig. 

 2, g,g, and fig. 10, c,d,ej,h,g). These are, in all British spiders, 

 six in number, with, in some families, a very short, broad, 

 supernumerary one, generally divided by a cross-line, and 

 placed immediately in front of the rest (pi. i., fig. 10, a,b). In 

 some exotic groups the numbers are also two and four. These 

 organs are the spinners, and they play a most important part in 

 spider economy, forming also (as stated before), one of the 

 leading characters of the order Araneidea. 



The position of the spinners varies; usually they are of 

 different sizes, longths, and direction, varying from one to three 

 joints. At their extremities, and sometimes along the under 

 surface of the last joint, are many minute tubes (spinnerets), 

 through which the silken lines issue ; these lines are, in part, 

 propelled at the will of the spider, and partly drawn from the 

 spinnerets by external influences. The silk is secreted in the 

 form of a gum-like fluid, iu small bulbous-shaped organs, situ- 

 ated within the under surface of the hinder part of the abdomen. 

 The silk emitted from the supernumerary organ above-men- 

 tioned is of a peculiar nature, and is drawn from it by means of 

 the " calamistra," noted in describing the armature of the legs. 



