While the Ixodinae only moult twice during their 
life, viz., at the change from larva to nymph, and again 
from nymph to adult ; the Argasinae moult not only 
at these periods but also several times during the 
nymphal stage and again several times during the 
adult stage. The Argasinae also do not become 
distended with blood to the enormous extent so 
characteristic of the Ixodinae. The duration of life 
is probably a year or more. 
External Anatomy 
Ixodinae 
The Rostrum or Capitulum .—The rostrum consists 
of a massive posterior portion (head) prolonged 
anteriorly into the mouth parts. 
The dorsal surface of the head is continuous, 
anteriorly, with two tubular sheaths (mandibular 
sheaths) within which the rod-like mandibles (or 
Cheliceres) play (Fig. 95). Ventrally, the head is 
continued forwards as a conspicuous dagger-shaped 
H 
Fig. 95. (Left figure). Mouth 'parts of Hyalomma (an Ixodine). 
(Right figure) Mouth parts of an Eurhipicephalus (a Rhipicephaline) 
H = hypos tome ; 1-4 = segments of palpi 
