266 



TROPICAL MEDICINE AND HYGIENE 



;. The rostrum projects from the anterior extremity 

 of the body. The palps are deeply grooved on their inner 

 aspects and act as a sheath to the rostrum. The last joint 

 of the palps is a small projection from the third. The second 

 joint is long in one division, Ixodinae (fig. 71), and shorter, as 

 broad as long, in another: Rhipicephalae (fig. 72). On the 

 dorsal aspect is a hard chitinous plate, dorsal shield, covering 

 the entire dorsum in the male but only the anterior part in the 

 female. The Ixodina are important as the carriers of piro- 

 plasma in the lower animals. They are not proved to carry- 

 any disease to or from man. 



FIG. 73. Mouth-parts of Argasina. 



ARGASIN/E differ from Ixodinae in that (i) the rostrum is 

 on the under surface of the body ; (2) the palps do not form 

 a sheath for the rostrum (fig. 73) ; (3) they have no dorsal 

 shields, but a thick leathery covering ornamented with knobs 

 or bosses, making a regular pattern. 



There are two genera : 



A rgas. Body with sharp edges. The pattern of the marking 

 close to the edge differs from that on the rest of the dorsum. 

 Species of this genus carry the avian spirochsetes. 



Ornithodorus. Body with rounded edges. No difference in 

 the pattern of the marking on the edge from that of the rest 

 of the dorsum. 



Ovnithodonis moubata carries Spirochata duttoni, the cause of 

 the African form of relapsing fever. 



