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XLVI] appeared on the West Coast of Africa for the first time about the year 1872. Since that date it has spread all over the tropical parts of that continent and even to some of the adjacent islands— Madagascar for example. As a cause of suffering, invaliding, and indirectly of death, it is an insect of some importance. It is now extremely prevalent on the East Coast of Africa, and is causing a large amount of invaliding amongst the Indian coolies there, by whom it has been introduced into India.

The chigger (Fig. 208) is not unlike the common flea (Pulex irritans) both in appearance and, with one exception, in habit. It is somewhat smaller in size—1 mm., the head being proportionately larger and the abdomen deeper than in the latter insect. In colour it is red or reddish brown. Like the

Fig. 209.—Chigger: impregnated female. (Blanchard.)

flea, its favourite haunt is dry, sandy soil, the dust and ashes in badly kept native huts, the stables of cattle, poultry pens, and the like. It greedily attacks all warm-blooded animals, including birds and man. Until impregnated, the female, like the male, is free, feeding intermittently as opportunity offers. So soon as she becomes impregnated she avails herself of the first animal she encounters to burrow diagonally into its skin, where, being well nourished by the blood, she proceeds to ovulation. By the end of this process her abdomen, in consequence of the growth of the eggs it contains, has attained the size of a small pea (Fig. 209). The first anterior and the two posterior segments do not participate in the enlargement, the latter acting as a plug to the little hole made by the animal when she entered the skin. When the ova are mature they are expelled and fall on the ground. In a short time a thirteen-ringed larva is hatched out from each egg. This larva presently encloses itself in a cocoon, from which, in eight or ten days, the perfect insect emerges.

During her gestation the chigger causes a considerable amount of irritation. In consequence of