62 
Parasitic Arthropods 
IxODOIDEA OR TlCKS 
Until recently, the ticks attracted comparatively little attention 
from entomologists. Since their importance as carriers of disease 
has been established, interest in 
the group has been enormously 
stimulated and now they rank 
second only to the mosquitoes 
in the amount of detailed study 
that has been devoted to them. 
The ticks are the largest of 
the Acarina. They are char¬ 
acterized by the fact that the 
hypostome, or “tongue” (fig. 45) 
is large and file-like, roughened 
by sharp teeth. They possess 
a breathing pore on each side 
of the body, above the third 
or fourth coxae (fig. 45 b). 
There are two distinct fami¬ 
lies of the Ixodoidea, differing 
greatly m structure, lite-history and habits. These are the Argasidae 
and the Ixodidae. We shall follow Nuttall (1908) in characterizing 
these two families and in pointing out their biological differences, and 
shall discuss briefly the more important species which attack man. 
The consideration of the 
ticks as carriers of disease 
will be reserved for a later 
chapter. 
Argasidae 
In the ticks belonging to 
the family Argasidae, there 
is comparatively little sexual 
dimorphism, while this is 
very marked in the Ixodidae. 
The capitulum, or so-called 
“head” is ventral, instead of 
terminal; the palpi are leg¬ 
like, with the segments subequal; the scutum, or dorsal shield, is 
absent; eyes, when present, are lateral, on supracoxal folds. The 
45 a. Argus persicus. Capitulum of male 
After Nuttall and Warburton. 
