62 



Parasitic Arthropods 



Palp article 4 

 Art. ? 



External jSrChi'l.ccra 



hypostcnte 



Shaft of 

 Chtlicera 



45a. 



Argus persicus. Capitulum of male 

 After Nuttall and Warburton. 



IXODOIDEA OR TiCKS 



Until recently, the ticks attracted comparatively little attention 

 from entomologists. Since their importance as carriers of disease 



has been established, interest in 

 the group has been enormously 

 stimulated and now they rank 

 second only to the mosquitoes 

 in the amount of detailed study 

 that has been devoted to them. 

 The ticks are the largest of 

 the Acarina. They are char- 

 acterized by the fact that the 

 hypostome, or "tongue" (fig. 45) 

 is large and file-like, roughened 

 by sharp teeth. They possess 

 a breathing pore on each side 

 of the body, above the third 

 or fourth coxas (fig. 456). 



There are two distinct fami- 

 lies of the Ixodoidea, differing 

 greatly in structure, life-history and habits. These are the Argasidae 

 and the Ixodidffi. We shall follow Nuttall (1908) in characterizing 

 these two families and in pointing out their biological differences, and 

 shall discuss briefly the more important species which attack man. 

 The consideration of the 

 ticks as carriers of disease 

 will be reserved for a later 

 chapter. 



Argasidae 



In the ticks belonging to 

 the family Argasidae, there 

 is comparatively little sexual 

 dimorphism, while this is 

 very marked in the Ixodidffi. 

 The jcapitulum, or so-called 

 "head" is ventral, instead of 

 terminal; the palpi are leg- 

 like, with the segments subequal; the scutum, or dorsal shield, is 

 absent; eyes, when present, are lateral, on supracoxal folds. The 



i5b. 



Left spiracle of nymph of Argas persicus. 

 After Nuttall and Warburton. 



