NOTES ON TICKS 39 



though in the tick-fever of Africa this is nearly certainly the case. 

 A fowl-tick, Argas miniatus, has been found to be intermediary in 

 spreading the spirillosis of *fowls, which in some ways resembles 

 relapsing fever in man. 



Ornithodorus moubata is now known to be the carrier of tick-fever 

 or relapsing fever in man in tropical Africa. In Mexico, -Florida, 

 and Texas an allied species, O. turicata, is fatal to fowls and harmful 

 to human beings. In Persia the Argas Persians attacks both poultry 

 and human beings, and its bite both in history and at the present 

 time is reputed to be injurious. Whether this is from a specific 

 infection or a common lymphangitis is not known. 



The relation of ticks to the piroplasmata will be considered in 

 the ensuing chapter. The tick Boophilus bovis, mentioned in Part I. 

 of this work as the carrier of the destructive piroplasmosis of cattle 

 called Texas cattle-fever, has been renamed Alectorobius by Pocock. 1 

 It belongs to the argas family. 



Ticks are divided into two distinct families the Argasida and 

 the Ixodida. The former have no dorsal shield, and the head or 

 capitulum is not seen from the dorsal aspect, being overlapped by 

 the body of the animal (see Fig. 9, C). Ticks differ from insects in 

 having four instead of three pairs of legs, and in the absence of 

 antennae and the lack of subdivision of the body into somites. The 

 adult females produce a great number often thousands of eggs, 

 which they deposit in clefts in the ground. The young ticks hatch 

 out with only three pairs of legs, the fourth pair not then being 

 formed. These young are termed larva. 2 They crawl upon the 

 stems and leaves of the grass and other vegetation, and, endowed 

 with a remarkable power of fasting, they wait, it may be for 

 months, before a suitable host brushes past or thrusts his muzzle 

 among them ; such as find a lodgment lose no time in piercing 



1 R. I. Pocock in Allbutt and Rolleston's ' Medicine,' vol. ii., part ii. 



2 The term 'larva 5 is thus seen not to be limited to a grub or caterpillar-like 

 creature, as is the case when we speak of insects. Such grubs pass into a chrysalis 

 or pupa stage, to emerge as a winged insect or imago. This is termed the meta- 

 morphosis. It is only observed in the higher insecta, and there is no such process 

 in the acarina. 



