MEDICAL ENTOMOLOGY 



as the month ring, and at this point the buccal cavity becomes 

 widened out. 



At the level of the first palpal segment the buccal cavity becomes 

 enclosed completely (fig. 3) by the dorsal and ventral integument of the 

 basis capituli, and about this level the basal end of the hypostome divides 

 into two processes, the posterior of which blends with the ventral body 

 wall, while the anterior is continued backwards as the ventral wall 

 of the buccal cavity (Plate LXXXV, fig. 1). In a median longitudinal 

 section a little to one side of the middle line (fig. 1) the buccal cavity 

 is seen as a long tube bayed out at. its posterior end; it is bounded 

 dorsally by the mandibular sheaths and the mandibles, ventrally by 

 the hypostome, and laterally by the strong fold of integument formed by 

 the junction of the sides of the hypostome with the skin of the last palpal 

 segment (fig. 3). The posterior end is closed by a strong bar of chitin 

 formed by the internal extension of the basal joint of the palpal segment 

 and by the base of the hypostome ; from the posterior surface of this bar 

 a horizontal plate of chitin projects backwards into the anterior end of 

 the body cavity (Plate LXXXIII, fig. 3), dividing it into two compart- 

 ments. The bulbous ends of the mandibles lie on the plate in the dorsal 

 compartment and the pharynx lies in the ventral. The salivary ducts 

 enter the mouth ring at the sides of the plate which supports them, and 

 open into the sides of the bayed-out end of the buccal cavity. 



Samson, in her account of the buccal cavity of Ixodes riciiuis, figures 

 and describes an elastic flap of chitin which extends forwards from the 

 ventral wall of the buccal cavity and divides it into two portions. She 

 regards the dorsal chamber into which the salivary ducts open as the 

 salivary receptacle ; the ventral chamber contains the opening of the 

 pharynx or pumping organ. She believes that the chitinous flap acts 

 as a valve, and that the saliva, as it flows from the ducts situated 

 above and behind it, presses it down and closes the opening into the 

 pharynx ; in this w r ay the saliva is prevented from passing directly into 

 the pharynx. 



The mouth parts of ticks are adapted for the purpose of piercing the 

 skin and at the same time fixing the parasites to their hosts. The 



mechanism may be studied by placing an unfed tick, 

 Mechanism of the u r i n1 ,, , " , 



mouth parts sucn as a female Rnipicepnains sangiiuteits, on the ear 



of a dog. After moving about for a short time, feeling 

 the skin with the ends of the palps, the fourth segments of which are 

 armed with well developed sensory hairs, a suitable spot is selected and 

 the mouth parts lowered. The palps are then everted, and a firm hold 



