CHAPTER XIII 



THE TICKS 



There has been considerable difference of opinion among various 

 authors as to the systematic arrangement of the ticks. They have 

 been brought into one family, — Ixodidse, in which two subfamihes are 

 distinguished, — Argasinse and Ixodinae, and, again, these two subgroups 

 have been considered as distinct families. The arrangement adopted 

 here, which raises the ticks to the rank of a superfamily, is that of Banks 

 (1894) and as followed by Salmon and Stiles (1901). 



Structure of Ticks in General. — The proper study and differentiation 

 of the ticks requires some knowledge of the external parts and an under- 

 standing of the technical terms which are used in reference to them. 

 Conforming to the general characteristics of the order Acarina to which 

 they belong, the ticks have a body in which the cephalothorax and 

 abdomen are not demarcated and this bears certain structures possessing 

 variations as to location and form which serve as defining characters 

 for the various subgroups and species. The parts more commonly 

 referred to with their technical names follow : 



1. The Capitulum (Fig. 76) is the "head," "false head," or rostrum, as 

 it is variously termed. It projects from the anterior extremity in the 

 Ixodidse. In the Argasidse, except in the larval stage, it is upon the 

 under surface of the anterior extremity. The structure consists of a 

 number of parts, as follows : 



(a) The Basis Capituli (Fig. 76, b) is the hard base of the capitulum; 

 the basal ring or mouth shield. 



(b) The Hypostome (Fig. 76, h) or "labium" or "radula" of various 

 authors is a median ventral structure rising from the basis capituli and 

 bearing recurved teeth. 



(c) The Cheliceroe (Fig. 76, c), "mandibles," or "jaws" are paired 

 elongate structures, one on each side of the median line, lying dorsal 

 to the hypostome. Dorsal to these is the hood or sheath of the chelicerae. 



The hypostome, chelicerse, and hood constitute the haustellum, or, as 

 it is commonly called, the "beak," and it is these structures which pen- 

 etrate the skin of the animal upon which the tick attaches. 



(d) The Palpi (Fig. 76, p) are articulated structures, one on each 

 side of the haustelliim, and inserted antero-laterally upon the basis 

 capituli. 



2. The Scutum (Fig. 77), or dorsal shield — present in the Ixodidse, 



