L. B. Robinson and J. Davidson 
399 
nerve cells are of practically uniform size and agree in their appeai-ance 
with the “medium-sized” cells which Nordenskiold has described. 
The small ganglion cells do not appear to be represented in this species. 
Fig. 7. Argas persicus 3 . Transverse section of a portion of the ganglionic layer, from 
the ventral part of one of the pedal ganglia. 
bl.cp. blood corpuscle; g.c. ganglion cells; n.f. nerve fibres; nl.sh. neurilemma 
sheath; s. mol. molecular substauce; s.pg. periganglionic sinus. 
mm 
The Peripheral Nervous System. 
Seven pairs of' large nerve trunks arise directly from the central 
nervous system in Argas persicus, viz. 
1. The cheliceral nerves. 
The palpal nerves. 
The nerves of the 1st pair of legs. 
>i „ j > 2nd „ 
>> >} >) 3rd ,, » 
A.f v~> 
jj it ,, .. 
2 . 
3. 
4. 
5. 
6 . 
7. The splanchnic nerves. 
In addition to these, however, a variable number of small nerves 
arises directly from the brain, one group originating close to the bases 
of the palpal nerves, while the remainder are irregularly distributed 
along the posterior margin and are apparently associated with the 
splanchnic trunks (see Text-fig. 5). It is the presence of these smaller 
nerves, and the fact that the main trunks themselves may occasionally 
26—2 
