L. E. Robinson and J. Davidson 
395 
which he foiled to be distributed in the ganglionic layer of the central 
nerve mass 1 . A short but useful general account of the nervous system 
is to be found in Bonnet’s work on the comparative anatomy and 
development of ticks 2 . 
The Central Nervous System. 
The central nerve mass or “ brain ” of Argas persicus is situated in 
the anterior part of the body, immediately below the anterior margin of 
the stomach, i.e. the place where the latter organ bifurcates to form the 
antero-lateral coecal lobes. Its ventral surface rests upon the dorsal 
surface of the terminal portion of the genital tract—the vagina in the 
female, the ductus ejaculatorius in the male. The organ is traversed 
longitudinally by the oesophagus, which enters in front, some little 
distance below the anterior margin, and passing obliquely upwards 
outermost line, which follows the contour of the “brain” and is continued along the 
nerve roots, represents the periganglionic sinus. Slightly schematised. 
1 Nordenskiold, E. (1909 c), pp. 461-464. 2 Bonnet, A. (1907), pp. 26-34. 
