274 ENTOMOLOGY FOR MEDICAL OFFICERS 



latent and becomes active in some subsequent stage of the tick's existence 

 or in some subsequent generation. In some cases a female tick thus 

 infected transmits the infection to her eggs, so that in due time the 

 larvae from these eggs are infective. In this way one of the worst and 

 commonest of the cattle-fevers due to piroplasms may be spread by the 

 larvae oi Boophilus and other ticks. In other cases, where the specific 

 blood-parasite has a longer term of development, the larvae hatched from 

 infected eggs are not infective, nor are the nymphs into which they 

 transform ; though both larva and nymph are infected. Here, as 

 Lounsbury has shown, the development of the specific parasite is not 

 complete until the generation inheriting the infection has become adult, 

 and it is the adult that is infective. In this way a malignant jaundice in 

 dogs, due to a specific piroplasma, is transmitted by adults of a 

 Hamaphysallis and a Rhipicephalus that have inherited their infection 

 from their female parent. 



There are other possibilities, as where a larva or a nymph imbibmg 

 blood from an infected animal incubates the infection and becomes 

 infective in the stage immediately following — the larva when it becomes 

 a nymph ; the nymph when it becomes adult. 



A tick once infected appears to be actually or potentially infective for 

 the rest of its life. Nuttall has found the piroplasma of malignant 

 jaundice of dogs in a Hamaphysallis after seven months' starvation, and 

 he thinks it possible that an infected tick (presumably inheriting its 

 infection) may transmit the infection to its offspring even though it itself 

 should feed on a healthy animal. 



Synopsis of Genera of Ixodinae. 



rAnal groove arching anteriorly ; ventral surface of male entirely 

 covered with chitinous plates ; no eyes Ixodes. 



I Anal groove, if present, arching posteriorly ; ventral surface of 

 male not entirely chitinous = 2. 



(Rostrum long ; in any ambiguous case the coxas of the fourth pair 

 of legs are not much larger than any of the other coxas = 3. 

 Rostrum short ; in any ambiguous case the coxas of the fourth pair 

 of legs are particularly large = 5. 



/No eyes; no adanal plates Aponomma. 



\Eyes present = 4. 



(Stigmata triangular with rounded angles. No adanal plates 

 Amblyomma. 

 Stigmata comma-shaped. Adanal plates in male Byalomtna. 



(No eyes ; 2nd segment of pedipalps laterally angulated or acute. 

 No adanal plates Hamaphysallis. 



Eyes present ; 2nd segment of pedipalps not laterally acute = 6. 

 rCapitulum quadrangular j no adanal plates = Dermatocentor. 



6. -j Capitulum hexagonal ; no adanal plates = Rhipicentor 



I Capitulum hexagonal ; adanal plates in male = 7. 



