400 
Argas persicus 
divide into two branches immediately at their point of issue from the 
brain, that has given rise to the discrepancies in the literature. Heller, 
for instance, alludes to the presence of 18-19 nerve trunks radiating 
directly from the brain in Argas persicus 1 , and in Ixodes ricinus, 11 
pairs of nerves were described by Pagenstecher 2 . Heller also found a 
median unpaired nerve which took its origin from the anterior part of 
the brain and ran forwards beneath the oesophagus to the mouth- 
parts, but, so far as we know, nobody has since succeeded in confirming 
this observation. 
The structure of the nerves is apparently simple. Each trunk is 
closely invested by a thin neurilemma sheath which is continuous with 
that of the brain. Immediately below the neurilemma, large elliptical 
nuclei are distributed at intervals, which rest on the external surface 
of a central core of fine longitudinally-disposed nerve fibrils, the latter 
forming the greater part of the mass of the nerve. It has been 
previously shown that each of the main nerve trunks runs, freely 
suspended, within the lumen of an arterial branch of- the periganglionic 
blood sinus (see Part II, pp. 243-244). 
The cheliceral nerves arise from the antero-dorsal extremity of the 
supraoesophageal portion of the brain, and immediately beyond the 
point of origin each nerve runs directly upwards to the proximal 
extremity of the shaft of the corresponding chelicera, where it divides 
into two branches, one of which enters the base of the shaft and 
innervates the digital muscles, while the posterior branch ramifies 
among the retractor muscles. 
The palpal nerves take their origin from the antero-lateral angles of 
the brain, on either side of the oesophagus. They run forwards along¬ 
side the pharynx, near the posterior end of which each gives off a 
mesial branch which runs towards the middle line of the body and 
loses itself among the pharyngeal muscles, while the main branch 
continues to the base of the palp which it enters. 
The four pairs of pedal nerves spring from the lateral margins of the 
brain, each trunk passing outwards to its respective appendage. Each 
pedal nerve divides into two equal branches at a point about mid-way 
between the brain and the coxa. 
The splanchnic nerves originate from the postero-lateral angles of 
the brain, from which they pass almost directly backwards, their branches 
innervating the alimentary canal, the genitalia and the body-muscles. 
1 Heller, C. (1858), p. 311. 
3 Pagenstecher, H. A. (1861), p.'36. 
