30 



from the host and armed with recurved teetli. On each side of the 

 hypostome are the mandibles or chelifers, also barbed. The whole 

 constitutes the rostrum (PI. X, fig. 3), and is highly developed even 

 in the earliest stage after hatching. It will thus be gathered that the 

 food of the tick is exclusively the blood of the host. Eyes are present 

 in some genera and not in others, or else a*re rudimentary. Respira 

 tion is said to be tracheal, and on each side of the body near the 

 fourth pair of legs there is a spiracle or peritreme, with a central 

 stigma (PI. X, fig. 5), though why this is absent in the larval stage 

 is not quite clear. 



The sexual organ of the female is situated far forward, between 

 the leg bases, and is absent in both larval and pupal stages. 



The reproductive organs of the male 1 will refer to later on. The 

 anus is situated lower down on the ventral surface and surrounded 

 in part by a groove, the contour of which is an important factor in 

 determining genera and species, as to whether this groove encircles 

 the anus in front or behind. The second pair of legs is the shortest, 

 as the fourth pair is the longest. The feet have two claws, and in 

 the young a membranous pad or pulvillus. On the tarsus of the 

 first pair of legs there is a structure called Haller's organ (PI. X, 

 fig. 4), whose function is little understood, but is supposed to be the 

 seat of some special sense of touch, hearing, or smell. The integu- 

 ment has a curiously striated appearance under a high power. 



The super-family of the Ixodoidea comprises the families Arga- 

 sidce and Ixodidte^ the distinguishing features of which are mainly 

 as follow : 



In the IxodidiB the dorsal surface of the male, except for a narrow 

 margin, is covered by a shield or scutum, which prevents any large 

 degree of distension, whilst in the female (which is the larger) it is 

 a small patch on the anterior part of the dorsum, the rest of the body 

 being capable of enormous distension after feeding (PI. X, fig. i). 



In the Argasidce there is no scutum, the body being covered by a 

 more or less horny integument. 



Other differences are as follow : 



ArgasidcE. Ixodidcc. 



Sexual dimorphism . . Slight . Marked. 



Capitulum . . . Ventral, . Anterior, 



under shield . projecting beyond shield. 

 Scutum .... Absent . Present. 



Festoons (or abdominal 



margins) . . . Absent . Generally present. 

 Spiracles .... Very small . Large. 



Legs .... Without spurs . With spurs. 



Pad or pulvillus . . Absent . Present. 



The Argasidce are much larger than the Ixodidce, live several years, 

 feed moderately, lay a few eggs in small batches, have two or more 

 nymphal stages, and moult frequently, whilst the Ixodidce do not live 

 more than two years ; the females, as before mentioned, when gorged 



