iii. INTRODtTOTION. 



determination of spiders, never being exactly alike in any two 

 males of different species. 



The development of the palpal organs is the sure criterion of 

 maturity. 



The Sternum. 



This has already been mentioned as the plate to which the legs 

 are articulated (pi. i., fig. 2d). It is usually flat or sub-convex ; 

 its shapo is either round, oval, oblong, or heart-shaped, and it 

 forms the under surface to the cephalo-thorax. At its fore 

 extremity is a sort of narrow continuation of it, forming 

 The Labium. 



This constitutes the completion of the mouth parts by stop- 

 ping up the gap between the maxillse (pi. i., fig. 2c). It 

 is divided from the sternum by a groovo or suture, but is 

 never articulated to it. It is sometimes projected in the same 

 plane as the sternum, but is more often set at a greater or less angle 

 with it, following, in fact, the direction of the maxilla) and 

 falces. The labium is of great importance to the spider, for 

 without it the juices of its prey would escape, instead of being 

 retained and guided into the throat, by the assistance of the 

 "tongue" (a small obscure portion of structure immediately 

 between the labium and falces). The length and form of the 

 labium is different in different spiders ; usually it is either 

 semi-circular, sub-triangular, oblong, or quadrate ; its apex is 

 often pointed, and sometimes emarginate. PI. ii., fig. 2cf., shows 

 the labium of Ati/ptis, and fig. Id that of Segestria. 

 The Abdomen. 



We come now to tho second leading division of the spider's 

 body — the abdomen. This is attached to the hinder part of the 

 cephalo-thorax by a short, but distinct, sheath or pedicle. It 

 is of diverse form in different spiders, round, oblong, globular, 

 flattened, quadrate, or sub-triangular. Various humps, 

 prominences, and othor eccentricities of form are found on the 

 abdomon in some exotic spiders, and, in a lesser degree, in several 

 of our British species — Cyclosa conica, Pallas (pi. iv., figs. 6, 6«). 



