. Des parasites animaux et la maladie humaine. Les insectes vecteurs ; parasites ; les maladies parasitaires ; parasitologie médicale ; insectes en tant que porteurs de la maladie. L'HISTOIRE DE LA VIE 355 La vie de tous les tiques sont plus ou moins semblables. Après plusieurs jours de l'accouplement la femelle les tiques et engorge peu après tomber au sol et commencent à pondre leurs oeufs (Fig. 153). Ce sont déposés sur ou juste sous la surface du sol. Certains de la famille Argasidae engorge plusieurs fois, portant un lot de de 20 à 50 œufs après chaque repas gourmand. Tous les Ixodidse, d'autre part, déposent leurs œufs après une seule engor

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. Animal parasites and human disease. Insect Vectors; Parasites; Parasitic Diseases; Medical parasitology; Insects as carriers of disease. LIFE HISTORY 355 The life histories of all ticks are more or less similar. After several days of mating the female ticks engorge and soon after drop to the ground and begin to lay their eggs (Fig. 153). These are deposited on or just under the surface of the ground. Some of the family Argasidae engorge several times, laying a batch of from 20 to 50 eggs after each gluttonous repast. All of the Ixodidse, on the other hand, lay their eggs after a single engorge- ment. The eggs number from a few hundred in some species to upwards of 10, 000 in others and are laid in rather elongate masses in front of the female. Each egg as it is passed out by the ovipositor is coated with a viscid substance by glands between the head and dorsal shield of the tick and is then added to the mass in front. The process of egg-laying occupies several days, as not more than several hun- dred eggs can be passed out and treated with the viscid coating in the course of a day. The eggs develop after an incubation period which varies with the temperature from two FlG 153 Texas or three weeks to several months. Eggs de- fever tick, Margaropus posited in the fall do not hatch until the fol- aJ^£ Graybin.) eggS' lowing spring. The larval ticks which hatch from the eggs are much smaller than the adult ticks and have only six legs (Fig. 157B). They are popularly known as " seed ticks." The seed ticks soon after hatching climb up on a blade of grass or bit of herbage and assume a policy of watchful waiting until some suitable host passes with- in reach. Seed ticks must be imbued with almost unlimited patience, since in many if not in the majority of cases long delays must fall to their lot before a suitable host comes their way like a rescue ship to a stranded mariner. The jarring of a footstep or rustle of bushes causes the ticks instantly to stretch out

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