Ticks and Disease. 
277 
its liairs as it brushes past. They quickly obtain a secure hold 
upon the skin, gripping it with the claws with which their 
feet are well provided, and, plunging in their beaks, greedily 
begin to suck in the blood. The beak or rostrum is a compli- 
cated organ studded with hook-like teeth, which serve to 
anchor the parasite more firmly ; indeed, 
if a tick is forciblv removed the rostrum 
•> 
is almost certain to be left behind, often 
causing a suppurating wound by its con- 
tinued presence, and it is always desirable 
to induce a tick voluntarily to release 
its hold rather than to use violence in 
removing it. 
When the larva has filled itself with 
blood it withdraws its rostrum, unhooks 
its claws, and drops to the ground, and, 
crawling into some crevice, remains inert for a varying period, 
during which the food it has imbibed enables it to advance 
another stage in its development. When the change is 
complete, the skin splits and is cast off, and the “nymph” 
emerges. A blade of grass or a bush is again ascended and 
the waiting game recommences, for another full meal is 
necessary before further progress can be made. The whole 
structure of the animal is 
wonderfully adapted to the 
conditions of its life, for its 
patience is inexhaustible and 
its ability to continue to live 
without food amazing, and it is 
very certain that no chance of 
attaining another host will be 
let slip. 
The nymph, if it be lucky 
enough to find the animal it 
seeks, acts as did the larva. 
When full of blood it releases 
its hold and falls to the ground 
again, remaining quiescent 
until the change to the adult 
form is complete. Then another moult takes place and the 
newly emerged male or female once more seeks another host, 
on which it gorges itself and finds its mate. Eventually the 
gorged and fertilised female again drops to the ground to lay 
its eggs, and the life-cycle is accomplished. 
The foregoing is a brief account of what is probably the 
ordinary mode of life of a tick, three different “ hosts ” being 
visited in the course of its development. In the case of a few 
Fig. 6.— Nymph of 
Ixodes ricinus. 
