342 THE ARACHNOIDS 



tend to leave its habitation it may be transported in the bundles of native porters. 

 The transmitting agent of the north African relapsing fever and probably of the 

 Indian type is the louse. The body louse deposits about 75 eggs in the clothes of the 

 host, which hatch out in about four days and become adults in about two weeks. The 

 head louse deposits its eggs or nits on the hair of the host's head. (See Pediculus.) 

 O. savignyi has two pairs of eyes near base of mouth parts. 



Subfamily Ixodinae. Mouth parts project in front* of body when 

 viewed dorsally. Scutum present. Stigmal plates posterior to fourth 

 pair of legs. Adults have suckers beneath claws. Skin finely striated. 



Anus behind middle of venter. 



Sexual dimorphism marked. Male has well- developed scutum; 

 female has porose areas. 



Section Ixodae. Transverse recurved preanal groove in female. Male has ventral 

 surface covered with chitinous plates. No eyes. Genus Ixodes. 



Ixodes has long rostrum with slender palpi palpi narrow at base, leaving gap 

 between them and hypostome. 



Section Rhipicephalus. No preanal, but postanal groove in female. Ventral 

 surface of male without adanal plates in Dermacentor, Hcemaphysalis^ Aponomma 

 and Amblyomma, but with one or two pairs in Hyalomma, Rhipicephalus and 

 Margaropus. 



In the genera Hyalomma, Aponomma and Amblyomma the palpi are long and 

 slender and of about uniform width of segments. 



In Hyalomma the segments of palpi are of about equal length. In Aponomma 

 and Amblyomma the second palpal segment is much longer than the others. Ambly- 

 omma differs from Aponomma in being very ornate and in having eyes. 



In the genera Hcemaphysalis, Dermacentor, Rhipicephalus, and Margaropus the 

 palpi are short. 



Hcemaphysalis has very broad rostrum, triangular palpi, and no eyes. Derma- 

 centor has a square rostrum with short thick palpi, the second and third joints being 

 as broad as long. Dermacentor andersoni transmits spotted fever of the Rocky 

 Mountains not D. reticulatus. The most important characteristic of the genus 

 Dermacentor is the large size of the coxae of the fourth pair of legs. 



Rhipicephalus has palpi without transverse ridges and comma-shaped stigmal 

 plates. The stigmal plates of Margaropus are nearly circular and the palpi have 

 acute transverse ridges externally. Margaropus annulatus transmits Texas fever 

 of cattle. This tick is also called 'Boophilus bovis or B. annulatus. Some authors 

 term it Rhipicephalus annulatus. Larvae developing from eggs of female ticks 

 which have fed on cattle infected with Texas fever transmit the disease which is due 

 to a protozoon Babesia bigemina. 



PENSTASTOMIDA (TONGUE WORMS) 



These are vermiform acarines more or less distinctly annulated. They have 

 retractile hooks at either side of the elliptical mouth. 



