248 
Argas persicus 
outgrowths of the hypodermis, suggest a rudimentary “ book-gill ” 
formation. A small muscle which originates on the inner surface of 
the dorsal body-wall is inserted into the wall of the atrium near its 
base. This muscle appears to act as a dilator of the atrium, and is 
evidently homologous with the columellai' vinscle of the .spiracle of 
Haeniaphysalis pimctata. 
The main tracheal trunks (see Text-fig. 7), usually five in number, 
open from the lower or innermost extremity of the atrium; and almost 
from their point of origin they diverge, each to follow its respective 
course in the body of the tick. The distribution of the five trunks is 
as follows : 
(1) A large cmtenor' trunk (tr. ant.) runs directly forwards along 
the ventral body-wall and passes beneath the salivary gland where it 
Fig. 7. Argas persicus ? . Diagram showing the mode of origin and the disposition 
of the principal tracheal trunks, x 30 diam. 
divides into a large number of branches, some of which run towards the 
middle line of the body where they form an anastomosis beneath the 
brain with corresponding branches from the opposite side of the body. 
Other branches are distributed to the oesophagus and pharynx, the 
capitulum and its appendages, the first pair of legs and the anterior 
part of the body generally. 
(2) An antero-median trunk {tr. ant. med.) which supplies branches 
to the second, third and fourth legs and the coxal muscles, other 
