394 
Argas persicus 
the dorsal surface of the body, some distance posterior to the origins of 
the retractor muscles of the chelicerae. From the dorsal integument, 
they run downwards and forwards as a pair of stout muscular columns 
which, after passing beneath the posterior margin of the last pair of 
mesial intercoxal muscles, are inserted along the grooves which define 
the lateral margins of the post-genital area. From their relations with 
the terminal portion of the genital canal, it would appear that their 
function is principally concerned in the operation of oviposition in the 
female and the extrusion of the spermatophores in the male. 
The muscles of the walls of the genital tract reach a high state of 
development in the female, but their detailed description will be more 
conveniently dealt with in connection with the genitalia. 
The Nervous System. 
See Part II, Plates XIV-XVI. 
The nervous system of Argas persicus conforms essentially to the 
Aca?Hne type, in the fact that the entire central portion is fused into a 
single large ganglionic mass which surrounds the oesophagus, and from 
which the whole system of peripheral nerves takes its origin. 
As far as it was possible to study the structure of such small 
structures by fine dissection alone, the nervous system of this species 
was worked out by Heller 1 , and, though his description is somewhat brief, 
present knowledge has but little to add in amplification or modification 
of his observations. Pagenstecher described the nervous system in two 
species of ticks— Ixodes ricinus in the one case 2 , and Argas reflexus in 
the other 3 ,—but, beyond the fact that he established the number and 
arrangement of the nerve roots which arise from the central nerve mass 
with more accuracy and precision than Heller, his investigations do little 
more than confirm previous knowledge. 
Concerning the finer anatomy of the central nervous system in ticks, 
the earliest work with which we are acquainted is that of Wagner 4 , who, 
in his researches on the embryology of Ixodes calcaratus Bir., made 
some interesting observations which will be referred to later. For the 
most recent and detailed account of the histological structure we are 
indebted to Nordenskiold, who, in his investigations on the anatomy and 
histology of Ixodes ricinus, describes three distinct types of nerve cells 
1 Heller, O. (1858), p. 311. 
3 Pagenstecher, H. A. (1861 c). 
2 Pagenstecher, H. A. (1861). 
4 Wagner, J. (1894). 
