32 
Argas persiciis 
of which is directed towards the basis capituli. The extremities of the 
anterior lip are joined by a transverse fold of integument which com¬ 
pletes an elliptical figure, and which covers the hinder portion of the 
posterior lip, in such a manner as to make it appear that the latter 
protrudes through a gaping opening from the interior of the genital 
canal. There is no trace of an intromittent organ; in coitus, the 
function of such an organ is performed by the capitulum. 
The earliest trace of a genital orifice is seen towards the latter end 
of the second nymphal stage {deuteronymph), by which time a small 
dimple-like depression is found to occupy the site of the genital orifice 
of the adult. 
The Anus. 
Plate I, fig. 2 ; Plate II, fig. 4 ; and Plate III, fig. 5. 
In all the stages, the anus is situated in the median line, near, but 
slightly posterior to, the centre of the ventral surface. It has the form 
of a short longitudinally disposed slit (see PI. Ill, fig. 5, an.ap.), the 
margins of which are supported by a pair of stout anal valves {an.v.). 
The whole structure is surrounded by a slightly raised annulus (an.m.) 
of thickened cuticle, which gives it a more or less elliptical contour, 
the major axis of which is longitudinal. In the immature stages, the 
contour of this anal annulus approaches a more circular form, and the 
transverse diameter occasionally may slightly exceed the longitudinal. 
The anal valves, which have a semilunar form, are merely thickened 
portions of the cuticle, to the internal surface of which the anal muscles 
are attached. Towards their straight, mesial margins, they bear an 
irregular row of hairs, variable in number, which overhangs and guards 
the anal slit. In the larva, only a single pair of these anal hairs is 
developed. The cuticle is continued tln’ough the anal opening and 
forms a continuous, but very thin, chitinous lining to the anal canal. 
The actual lips of the anal slit are formed by the slightly prolapsed 
folds of this delicate cuticle which are seen between the anal valves. 
The valves are freely articulated to the anal annulus by the intervening 
thin soft cuticle. 
The Spiracles. 
Plate II, fig. 4, sp.; and Plate III, fig. 6. 
The spiracles are situated on the outer slope of the supracoxal 
folds, on a level with the bases of the coxae of the fourth pair of legs. 
Compared with the spiracles of the Ixodid ticks, they are small and 
