X11 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 compleated, 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,¢), is often observable, 
projecting between the anterior spinnerets. The “anal tubercle ” 
(Fig. 174, at), 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- 
heving 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.1 
_ The paturon is a stout joint of more or less cylindrical or 
conical shape. The unguis (the “ crochet” of Simon) is hook-like, 
1 Mém. Mus. d’ Hist. Nat. xviii., 1829, p. 377. 
