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ENTOMOLOGY FOR MEDICAL OFFICERS 



The hypostome (Fig. 120), which lies ventral to the 

 chelicerae and is a prolongation of the ventral lip of the 

 basis capituli, is armed on its ventral surface with files of 

 strong recurved teeth ; it aids the chelicerae in boring through 

 the skin of the victim and making good the hold. 



The pedipalps form an adjustable sheath to the more 

 delicate mouth-parts just described, and are frequently 

 hollowed along their inner surface for this purpose ; when 

 the mouth-parts are in action the pedipalps are, as a rule, 

 bent aside. 



The integument may be hard, or merely tough, or may 



Fio. 120. — Kostrum of a Tick ; left half of hypostome removed. 



be comparatively soft with localised chitinous indurations ; 

 embedded in it there are small glands, whose secretion is 

 possibly acrid and defensive, and sparse hairs. 



On the ventral surface of the body the four pairs of legs 

 are attached by broadly sessile coxae. Each leg consists of 

 6 segments (including the coxa), of which the last, or tarsus, 

 is as a rule incompletely subdivided into two pieces, as also 

 may be the 3rd segment, or femur ; the tarsus ends in a pair 

 of claws, which are borne on a slender stalk, with in some 

 cases a membranous plate, or pulvillus, between them. In 

 the cuticle of the extensor border of the tarsus of the first 

 pair of legs there exists a narrow-mouthed pit lined with 

 sensory hairs ; this, which is known as Haller's organ, was 



