[53] Adaptation of Ticks 331 



a host. During their long period of parasitism as nymphs they have 

 doubtless undergone internal changes leading to maturity, otherwise 

 they would not emerge so rapidly as adults from the nymphal skin. 

 The adults, without further feeding, mate ; the females oviposit in the 

 chinks and crevices, and the larvae which emerge from the eggs await 

 the coming of a host. Hooker, to whom we are indebted for most of 

 what is known of this curious life-history, very naturally regards the 

 habits of this tick as correlated with its peculiar form of parasitism in 

 the ears of its hosts. He does not, however, discuss the subject. 



Animals rubbing their ears or heads against infested posts or trees 

 ("rubbing places") would necessarily pick up the waiting larvae. 

 I would add that the structure of the mouth-parts, and especially 

 the presence of an unarmed hypostome in the adults, indicate that 

 they can scarcely be blood-suckers. It would be a matter of consider- 

 able interest, it seems to me, to examine the internal anatomy of the 

 adults of this species to see in how far it is modified, especially with 

 regard to the pharyngeal pump, salivary glands and digestive organs. 



The life-history of 0. megnini is that of an animal highly specialized 

 to a life of parasitism chiefly in the ears of its hosts. The larvae issue 

 from eggs laid on rubbing posts or trees, and the like, some feet above 

 the surface of the ground, so that they may readily gain access to the 

 heads of their hosts. The larvae enter the ear unperceived. It would 

 be a matter of increasing difficulty for succeeding stages to "cast anchor 

 in such a small harbour " a second time for, apart from their increasing 

 size, which would militate against their re-entering the ear, the number 

 of ticks of later stages which survive even from a large batch of larvae 

 (in all species of ticks) is very small and grows progressively smaller 

 toward the period when maturity is reached. The tick, having entered 

 the ear where it is safe for an unlimited time, takes advantage of the 

 protection afforded and only leaves it once when it abandons it as 

 a large nymph almost ready to cast its skin and emerge as an adult. 

 The period of parasitism as a larva is normal, but that of the nymphal 

 stages inordinately prolonged so that the tick only needs to go in and 

 out once through the small aperture of the ear. It is owing to the 

 choice of the ear for its place of feeding upon the host that the life- 

 history of this tick has become so peculiarly modified. Its spiny 

 integument, to which it owes its name of " spinose ear tick," may be 

 of use in connexion with its parasitism in the ear in lessening its 

 chances of adhering with a large body-surface to the cerumen within 

 the ear. 



22—2 



