ACAKUS SCABIEI. 29 



galleries are burrowed out by females after the tliird chnfige of skin, 

 and by fecundated females; the longest (up to i" or more in 

 length) are for egg-galleries. The burrows of the young mites 

 are shorter, at the utmost \ r " in length, and pass obliquely from 

 the epidermis to the cutis ; the shortest galleries (mere holes) 

 are those of the males. The burrow of the galleries corresponds 

 with the breadth of their inhabitants ; old galleries become nar- 

 rower by their walls approaching each other more towards the 

 entrance. The direction of the galleries, which is probably deter- 

 mined by the direction and depth of the furrows of the epidermis, 

 varies ; it is sometimes straight, sometimes tortuous, sometimes 

 angular, sometimes bent and looped, so that the gallery intersects 

 itself. The entrance is generally free ; in the case of males before 

 copulation, sometimes covered with fragments of epidermis ; its 

 margins are sharply bitten out ; when the galleries are not too 

 long it serves at the same time as a means of egress. Galleries 

 after the third change of skin have a separate egress. The im- 

 pregnated females leave their galleries no more ; they constantly 

 burrow further onwards and die in its blind extremity. The 

 males also appear to die after copulation in the last gallery which 

 they have excavated. The larger galleries on the hand form 

 blackish punctured lines (which is due to the lodgement of dirt); 

 on the body these lines are whitish. The latter colour is due to 

 dried epidermic scales, but the points are round or cleft-like aper- 

 tures in the upper wall of the gallery (air-holes and apertures of 

 egress for the brood), which are never wanting in large galleries, 

 and which stand at equal or unequal distances apart. In the gal- 

 leries we often see cast skins and balls of excrement, longitudinally 

 rounded, slightly tubercular, dark-yellow or dark-brown bodies, of 

 about yj'" in length, and often caked together (Eichstadt), which 

 vary according to the size of the animal, and represent its excrement. 

 These would be the primary objective phenomena, which, how- 

 ever, very rarely occur alone, as Baum, Eichstadt, and Gudden 

 have seen, when all reaction and exudation keeps away. According 

 to the variable irritability and reaction of the skin, various 

 secondary objective phenomena associate themselves herewith, or 

 the immigration of the mite combines with other accidental cuta- 

 neous diseases of the individual. If certain cutaneous diseases 

 are endemic anywhere, a peculiar external form may, as it were, be 

 impressed there endemically upon the itch. As regards the former, 

 we must refer particularly to the quantity of exudation and the 



