272 ENTOMOLOGY FOR MEDICAL OFFICERS 



its host to the ground again, to continue its growth, and in 

 course of time — two weeks to several months, according to 

 temperature — moults into a nymph. 



The nymph resembles the adult in having four pairs of 

 legs and a pair of stigmata, but it has no genital pore. It 

 waits about, in grass and herbage, until an opportune host 

 appears, to which it attaches itself. After satiation it, as a 

 rule, drops to the ground again, and in course of time — some 

 weeks or months, according to temperature — moults into the 

 adult form. 



In a few species (the notorious Boophilus furnishes a good 

 example) the larva, when it has once found a host, completes 

 its development and attains the adult stage on that 

 individual host. In this case, of course, development is 

 uninterrupted and much less precarious, and is therefore 

 much quicker. 



Some ticks {Ixodind) are, in natural circumstances, short- 

 lived, the male dying after copulation and the female after 

 parturition ; others {ArgantincR) are comparatively long-lived, 

 the female producing batches of eggs periodically. But even 

 the Ixodince are tenacious if the normal tenour of their life is 

 checked ; several observers have kept them alive, unfed, for 

 three or four months, and Nuttall kept starved specimens of 

 Hamaphysallis alive for seven months. 



Ticks may be grouped in two subfamilies — Ixodince and 

 Argantince — which some authors prefer to regard as distinct 

 families. In the Ixodince the rostrum or capitulum is terminal 

 in all stages of existence; in the Argantince it is inferior in 

 the adult and subterminal only in the early larval stage. 



Subfamily IXODIN^ : Hard Ticks. 



In this subfamily more or less of the dorsum of the body 

 is protected by a chitinous shield, or scutum, and in the males 

 of some species there are chitinous plates on the ventral 

 surface also. The capitulum is altogether anterior, being 

 implanted in the front end of the body. Frequently the 

 posterior border of the body is regularly cut into fine 

 festoons, which are particularly distinct in the male. The 

 stigmata are large, and lie behind the coxae of the fourth pair 



