320 ARACHNIDA ARANEAE CHAP. 



and can generally be folded back upon the paturon, which often 

 presents a groove for its reception. The Theraphosid spiders are 

 distinguished from all others by the fact that the plane of action 

 of the chelicerae is vertical and longitudinal. The paturon pro- 

 jects forward in a line parallel with the axis of the body, and its 

 distal end can be raised or depressed, but not moved laterally ; 

 while the unguis in action has the. point directed downwards, 

 and, at rest, is applied to the under surface of the paturon. 



In other spiders the patura hang more or less vertically, 

 and while to some extent mobile in all directions, their principal 

 motion is lateral, and the ungues have their points directed to- 

 wards each other in action, and are applied to the inner surfaces 

 of the patura in repose. The plane of action in this case is also 

 more or less vertical, but transverse. 



The paturon is always extremely hard and strong. In Thera- 

 phosae of burrowing habits the distal end is furnished with a 

 group of povverful teeth, the " rastellus." The 

 groove for the reception of the unguis is often 

 guarded on one side or on both by rows of teeth, 

 the arrangement of which is frequently an im- 

 portant specific character. The inner anterior 

 border is also often furnished with a group of 

 stiff hairs or bristles. This powerful joint is 

 of use in crushing and expressing the fluids of 

 insects pierced by the ungues. 

 FIG. 177. Front The crescent-shaped unguis is tapering and 



view of Textrix , f * ,-, 



denticuiata. x smooth, except for the presence, on the posterior 

 about 10. 1, sur face, of one or two feebly dentated ridges. 



Caput ; 2, eyes; J . 



3, paturon, and Near its free extremity there is a small orifice 



4, unguis of cheh- i ea( jing ^ o the poison reservoir and gland. 



In the genusPAo/cws(see p.401) the chelicerae 

 may almost be regarded as chelate, the unguis being met by a 

 spiny projection from the inner anterior border of the paturon. 



Rostrum. On examining a spider, even under a dissecting 

 microscope, it will not be easy at first to discover the mouth. 

 Indeed, Lyonnet had almost come to the conclusion that Spiders, 

 like some Myrmelionid larvae, imbibed the juices of their prey 

 by way of the mandibles, before he found the orifice and gave 

 a remarkably accurate description of the adjacent parts. 



If a specimen be placed on its back, and the labium raised 



