Ticks and Disease. 
279 
Two genera, Avgas and Ornithodorus , differ so much from 
other ticks that they are placed in a different family, the 
Argasidse. They have no scutum, and no pads to their feet 
when adult. Their integument presents no hard plates, but is 
leathery in texture, and their mouth parts are more or less on 
the under surface, instead of being terminal. In Avgas the 
rostrum is so ventrally situated that it is completely invisible 
from above, and the back is studded with numerous more or 
less symmetrically arrayed circular depressions. There are no 
eyes. In Ovnithodovus the rostrum is more in front, so that 
the palps project beyond the front margin of the body. The 
skin is roughened by numerous raised spots, and some species 
possess eyes. 
Fig. 9 . — Argas reflexus , x 10. 
Avgas persicns has been proved to convey a spirochete 
disease to fowls, and is believed to communicate it occasionally 
to man. In South Africa a similar human disease has been 
traced to Ornithodovus moubata. 
The remaining eight genera belong to the family Ixodidae, 
which may be recognised by the presence of a scutum, and of 
pads as well as claws on the tarsi. The characters of these 
genera are briefly given below : — 
BMpice plia lus . — Palpi short, flat above ; base of rostrum hexagonal ; eyes 
present ; anal plates on the male ; stigmata triangular or comma-shaped. 
Boophilus . — Palpi very short, with the middle of the second and third joints 
transversely ridged ; base of rostrum hexagonal ; eyes present ; anal plates on 
the male ; stigmata circular. 
