TICKS OF THE BELGIAN CONGO. 



315 



distinguishable by the shape of the sexual orifice. In Argasidae the capitulum in 

 adults and nymphs is covered by the overlapping body, in Ixodidae it is terminal 

 and visible dorsally. 



dUiti 



Fig a 



■ fi^i^/^4 ^t/&WK4 



Fig. 2. Argasidae [Argas) (Nut tall 

 and Warburton, 1908). 



Fig. 3. Ixodidae {Amhlyomma ?) 

 (Nuttall and Warburton, 1908). 



At least four stages occur in the development of ticks : egg, larva, nymph and 

 adult. In Argasidae there may be two or more nymphal stages. The larvae in 

 both families are hexapod, eight legs only appearing in the following or nymphal 

 stage. The nymph resembles the adult (male and female in Argasidae and the female 

 in Ixodidae) but for the absence of the sexual aperture and secondary sexual 

 characters. 



1. ARGASIDAE. 



The Argasidae comprise two genera : Argas and Ornithodonis and, as far as 

 known to-day, are represented in the Belgian Congo by but one species Orniihodorus 

 mouhata (fig. 4), of which the adult usually measures about 8 mm. in length, but may 

 attain a length of 12 mm. The colour is dusty brown or greenish when aUve. The 







Fig. 4. Ornithodorus mouhata (Murray, 1877) $ : dorsal and ventral aspects (Nuttall, 1908). 



integument has a granulated appearance and the legs bear characteristic humps. The 

 species is eye-less. The largest nymphs resemble the adults. The first stage nymph, 

 when unfed, measures usually but 1 mm. in length, and has a yellowish colour ; in 

 appearance it recalls the adult. The species is important as the carrier of relapsing 

 fever of man in tropical Africa. (See further on p. 342.) 

 (C221) a2 



