SEVENTEENTH ANNUAL REPORT. 



397 



(7) Caudal appendage. — In some species, as in Boophilus australis 

 (fig. 62), a distinct chitinous caudal prolongation is present. 



(8) Legs. — The legs (fig. 68) are eight in number in the nymphs and 

 the adult males and females (octopod forms), and six in the larvae 

 (hexapod form). They are arranged in pairs, which are numbered I 

 to IV. They are composed of six articles united by artictdations. By 

 the formation of p>settdo-articidations the third article {feimir) and the 

 sixth article {tarsus) may divide into double articles, thus giving eight 

 to the entire leg. The various articles are named as follows, beginning 

 at the end near the body: 



First article^ or coxa, which lies flat on the body and is not movable; 

 in some forms it develops into large plaques, or shields. It may be 



Fig. 68.— Tarsus I, claws and pulvillum of Boophilus annulatus. Greatly enlarged. Original. 



provided with more or less prominent spurs., or teeth (fig. 62), in which 

 case it is often spoken of as dentate^ hidentate^ etc. 



Second article^ or trochanter., a short article, may be broader than 

 long. 



Third article, or femur, an elongate article, which by the formation 

 of a pseudo-articulation (at its proximal end, nearest the trochanter), 

 may present a double article. 



Fourth article, or tihia, elongate. 



Fifth article, oy protarsas, elongate. 



Sixth article, or tarsus, which may form a pseudo-articulation at its 

 proximal or at its distal end; it is the article the furthest r&moved 

 from the body and bears at its distal extremity a stalk with two 

 claws, which in the family Ixodidse bear on their ventral surface an 

 umbrella-like or disk-like membranous expansion known as the 

 pidvillum. 



The tarsi of the first pair of legs are also provided near their distal 

 extremity with a cupuliform sense organ, Haller'^s organ, which is 

 supposed to be an organ of hearing (fig. 68). 



The corresponding articles of the difl'erent pairs of legs are num- 



