40 
Argas persicus 
margin slopes obliquely backwards, so that in its lateral portion it 
barely surrounds the base of the external article. With the exception 
of a limited free margin, the hood is always in intimate contact and 
more or less fused with the surfaces of the digit. Its relations with the 
articles are clearly shown in the transverse sections through the digit 
(PL VI, fig. 2-5, a.-f.). In these figures, the hood is distinguished by the 
darker, stippled shading, the articles of the digit being indicated by finer 
stippling on a clear ground. The free margin of the hood is slightly 
sinuous, and its extreme portion near the tip of the internal article is 
markedly serrated, the serrations presumably facilitating the retraction 
of the hood during the operation of biting. 
In both sexes, and also in the immature stages, the foregoing 
description applies. Slight differences do actually exist, but are quite 
unimportant from the anatomical standpoint. 
The Palps. 
The second pair of appendages, termed palps, are borne on the 
antero-lateral angles of the basis capituli, one on either side of the 
medianally situated hypostome (see PI. IV, figs. 8, 9 and 10, p.). Each 
consists of a more or less cylindrical appendage comprised of four, freely 
mobile articles, the lengths of which are approximately equal. In the 
state of rest, they are usually doubled up, in the manner shown in 
figs. 8 and 9 (PI. IV). 
The first or hasal article (p.i.) is the largest in diameter and its 
length is about equal to its breadth. The proximal portion is partially 
telescoped into the large articulatory foramen in the wall of the basis 
capituli; while the plane of the distal margin inclines downwards from 
the mesial side to the lateral face, thus giving the article, as seen from 
the ventral aspect, a rhomboidal outline. The free distal edge of the 
basal article surrounds the proximal part of the third article like a collar. 
An interesting feature, to be referred to again, is the development of 
two, pronounced, salient, longitudinal ridges which delimit the mesial 
face of the article dorsally and ventrally. Both ridges thin out to a fine 
edge, which overlaps the adjacent median structures—the basal portion 
of the hypostome ventrally, and the bases of the cheliceral. sheaths 
posteriorly. In the ventral view of the female capitulum (PL IV, 
fig. 8), these ridges have been unfortunately omitted, but they are 
clearly shown in the transverse sections of the capitulum (see PL V, 
figs. 11-15). The mesial face of the article, the dorsal and ventral 
