340 georCtE h. f. nuttall. 



In only one species {HaemaphT/salis inermis of Europe) are the larvae and nymphs 

 known to be rapid feeders. As a rule both sexes are found together upon the host, 

 where they may occasionally be found in copulation, but in some Ixodidae {Ixodes 

 especially) the males do not feed. In the latter case the males, after emerging from 

 the nymphal skin, lie in wait for the females which drop off gorged from the host in 

 its burrow or nest. This difference in the behaviour of the sexes depends, as Nuttall 

 has shown, upon the habits of the host. Wandering animals usually have species of 

 ticks upon them which cohabit upon the host, whereas hosts with fixed habitats 

 (burrows or nests) more usually have only females upon them. A¥hereas the males 

 of Argasidae partake of a full meal of blood, as do the females, the males of Ixodtdae 

 feed very sparingly and chiefly it would appear on lymph, for w^e have failed to find 

 red blood corpuscles in their alimentary canals, although we have examined many 

 specimens. 



As a rule, larvae and nymphal ticks abandon their host after feeding, and, falling 

 to the ground, undergo metamorphosis to the next stage upon the ground. Such 

 ticks are known as three-host ticks, for they require to have access to a host on three 

 occasions, when they feed in the larval, nymphal and adult stages. Of the Congo 

 ticks, Amhly omnia hehraeum, A. variegatum and Haemafliysalis leachi may be taken 

 as examples of three-host ticks. Other ticks undergo one moult upon the host and 

 re-attach themselves to the same host when they emerge. An example of such a two- 

 host tick is RhipicephaJus evertsi, wherein metamorphosis from larva to nymph takes 

 place upon the host. In Boophilus, on the other hand, we have a one-host tick, for it 

 remains upon a single host throughout its development from larva to replete adult. 



As previously stated, the males of Ixodidae, when they feed, do so sparingly. All 

 the other stages imbibe a large amount of blood in relation to their size. In the males 

 the dorsal surface of the body is entirely covered with a hard scutum, whereas in the 

 other stages the scutum is small and only covers the anterior portion of the body, the 

 greater part of which is soft and consequently capable of great distension owing to its 

 elastic integument. Many ticks are incapable of further development if they do not 

 gorge to repletion ; in others, partially engorged larvae and nymphs give rise to small 

 nymphs and adults respectively. This accounts for the great variation in size observ- 

 able in certain species, of which Rhipicephalus appendicidatus and R. sanguineus may 

 serve as examples (figs. 18, 19, 25 and 26). Imperfectly gorged females frequently 

 lay sterile eggs, and the number of eggs they lay is less than normal according to the 

 degree of engorgement. 



The mechanism of the bite is similar in all ticks. The paired cutting organs, or 

 digits of the chelicerae, penetrate into the skin by means of their very sharp recurved 

 teeth. Each chelicera (fig. 48) consists of a tubular shaft protruding from the base 

 of the capitulum, and provided at its distal extremity with a cutting organ or digit. 

 The latter is moved laterally by means of two tendons, an internal tendon which 

 extends it and a more powerful external tendon which causes it to turn outward. 

 Reference to the figure will render it clear how the chelicerae penetrate the tissues of 

 the host when the tendons act alternately upon the terminal cutting organ with its 

 sharp recurved teeth. Situated ventrally to the chelicerae is the rigid hypostome, 

 bearing sharp recurved teeth. The hypostome is dragged into the wound inflicted 

 by the chelicerae and its teeth serve to anchor the tick to the host without further 



