APPENDAGES 319 



ridge, the epigastric fold (Fig. 174), and in the centre of this is 

 the genital opening. This is never visible until after the last 

 moult, and in the male is always a simple inconspicuous aperture. 

 This is also the case with the females of some groups (Theraphosae, 

 Filistatidae, Dysderidae, etc.), but in most cases there is a more 

 or less complicated armature, the " epigyne," the special design 

 of which is of great specific value. In its simplest form it is 

 merely a plate, usually of dark colour, with one or two apertures 

 (Fig. 174, ep), but in some families, notably the Epeiridae, it is 

 more complicated, and is furnished with a hooked median pro- 

 jection, the " ovipositor " (" clavus " of Menge), which is often 

 absurdly like a petrified elephant's trunk in miniature. 



The abdomen also presents on its under surface, usually to- 

 wards the posterior end or apex, a group of finger-like mammillae 

 or spinnerets. They are normally six in number, two superior 

 (or posterior), two median, and two inferior (or anterior). The 

 number is reduced, in most of the Theraphosae, to four, while a 

 few spiders possess only a single pair of spinnerets. These organs 

 are described more fully on p. 325. 



A small papilla, the " colulus " (Fig. 174, c), is often observable, 

 projecting between the anterior spinnerets. The " anal tubercle " 

 (Fig. 174, a.t), on which the vent is situated, terminates the 

 abdomen, and is generally in close juxtaposition with the posterior 

 spinnerets. 



Appendages. — The cephalothoracic appendages are the cheli- 

 cerae, the pedipalpi, and the four pairs of ambulatory legs. Those 

 of the abdomen are the mammillae or spinnerets. 



Chelicerae. — These are two-jointed appendages, articulated 

 immediately below or in front of the clypeus. They are the 

 " mandibles '■'' of many authors, but there is good reason for be- 

 lievino- that they are not homologous with the mandibles of 

 Insects. There is little agreement, moreover, with regard to the 

 names given to the two joints of which they consist. The term 

 " falx," often applied to the basal joint, is much more appropriate 

 to the sickle -like distal joint. Base and fang are tolerably 

 satisfactory, or we may avoid ambiguity by adopting the terms 

 " paturon " and " unguis " suggested by Lyonnet.^ 



The paturon is a stout joint of more or less cylindrical or 

 conical shape. The unguis (the " crochet " of Simon) is hook-like, 

 1 Mha. Mus. d'llist. Nat. xviii., 1829, p. 377. 



