The Itch-mite
A much more serious trouble is due to Sarcoptes scabiei—often called the Acarus—which gives rise to the disease known in England as the ‘itch’ and in France as the ‘gale.’
Fig. 35.—Sarcoptes scabiei. Female. × 180. Ventral view.
(From Bourguignon.)
Sarcoptes scabiei in both sexes is but little longer than broad. The female is, as usual, larger than the male. These mites are shaped very much like microscopic tortoises, of a pearly grey colour, passing at parts into a rusty brown. Of the four pairs of legs two run forward close to the head, and two point backwards. The integument is semi-transparent and strengthened by parallel folds, and bears many little bilaterally symmetrical protuberances and scales. There are also certain hairs which have some systematic value.
Fig. 36.—Sarcoptes scabiei. Male. × 300. Ventral view. The sucker on the fourth leg on the right is accidentally folded over the third leg. (From Bourguignon.)
The male is usually recognised by the fact that its third pair of legs terminates in a long hair, whilst the other legs end in pedunculated suckers.
Fig. 37.—One of the legs of Sarcoptes scabiei (× about 450), showing the stalked sucker and the curious ‘cross-gartering.’ (After Bourguignon.)