ACAEINA OR MITES. 



125 



meal it falls from the host to the ground again, and may remain 

 for some time without any food. It moults or oasts its skin 

 whilst on the ground, and becomes a nymph with eight legs, 

 but is not sexually mature. This nymph then gets on to 

 another host and feeds, then it falls to the ground again and 

 moults for a second time. The adult stage is then reached, and 

 the adult males and females wait until they can again crawl on 

 to another host. The female then becomes much swollen out, 

 being gorged with blood, so much so that the head and legs can 

 scarcely be seen from above. The male 

 only swells to a small extent. When the 

 female is fully gorged and fertilised she 

 falls to the ground and lays her eggs in 

 long masses (fig. 55). The act of copula- 

 tion is peculiar, the male inserting the 

 proboscis into the vulva of the female 

 and so injects the spermatophores. 



Thus some Ticks require three hosts 

 to complete their development (Rhipice- 

 pJialus appendiculatus) ; others, however, 

 only require one host (R. decoloratus), 

 the larva and nymph not falling to the 

 ground but moulting on the host. 



Others require two hosts {R. evertsi), 

 which remains on the host for the first 

 two stages. 



Some Ticks may live a long time even without food. The 

 writer has kept one, Ornithodorus mouhata, for over a year. 

 jSTormally the true Ixodidse are not long-lived, but under ab- 

 normal conditions they may be. Wheeler kept Ixodis ricinus 

 alive for two years, and a female which had no head and could 

 not have taken any food. The importance of Ixodidae is not 

 only on account of their blood-sucking habits, which cause 

 severe irritation to animals and birds and man, but especially 

 because of the part they play in the spread of such diseases as 



Fio, 55. — Female Ticik (a), 



LAYING Efjcs (E). 



