MECHANISM OF MOUTH PARTS : PHARYNX 661 



of the skin having been obtained with the legs, the tick makes a steady 

 forward thrust with its body, as a result of which the hypostome is 

 driven into the skin. At the same time the mandibles are protracted 

 and their digits extended, and the teeth brought into play. As the 

 forward thrust is continued the hypostome is driven deeper into the skin 

 until it is almost completely embedded. If an attempt is made to 

 remove the tick it will be found to be firmly attached, the attachment 

 being mainly due to the strong recurved teeth of the hypostome. This 

 function of the hypostome is well exemplified in the various species. 

 For instance, in the Argatini (Plate LXXXV, fig. 7), which feed rapidly 

 and then leave their host, the teeth are poorly developed in comparison 

 with those of the Ixodini (fig. 6) which remain fixed to the host for long 

 periods ; in the latter the teeth are formidable weapons and considerable 

 force is required to detach them. In some genera, for example, Haema- 

 physalis, though the teeth are Well developed, the hypostome is short 

 and the tick is never able to obtain such a firm hold as in the species of 

 Ainblyomma, Hyalomma, and more particularly Ixodes, in which the 

 hypostome is long and is armed with many rows of strong projecting 

 teeth ; for this reason Haemaphysalis is readily detached and therefore 

 usually selects those parts of the skin where the host cannot very well 

 scratch it off. 



The hypostome is to be regarded as the fixing organ, and is not with- 

 drawn or moved once the tick is fixed ; the mandibles on the other hand 

 are the true cutting organs, and they are only brought into further action 

 when suction begins. The mandibles appear to be very similar in 

 action to those of the Orthorraphic Diptera ; protraction and retraction of 

 the shaft, together with extension of the teeth on the digits, results in a 

 saw-like movement which tears a hole in the skin. When the pumping 

 action of the pharynx, to be described presently, comes into play the blood 

 is drawn into the intestinal tract. The flow appears to be intermittent 

 in the case of the Ixodini, a small quantity only being taken in at first ; 

 when the tick is fertilized it fills up in a short time, and then withdraws 

 its mouth parts and crawls away. 



The irritation produced by the penetration of the mouth parts into the 

 skin, or the action of the salivary fluids, appears to produce in some 

 species an inflammatory reaction which results in the whole of the 

 capitulum being buried in scar tissue ; this is commonly seen in the case 

 of the male Hyalomma aegyptiinn. 



The pharynx consists of chitinous plates welded together to form a 

 long fusiform tube, which acts as the pumping organ. At the anterior 



