ACARUS SCABTET. 39 



two ventral surfaces are in contact, the dorsal surface of the 

 female touching the corresponding spot of the upper, and that 

 of the male the lower wall of the canal. To judge from cor- 

 responding proceedings in other mites, however, the male only 

 passes with a small portion of his abdomen under the end of the 

 belly of the female, and would have no hold during the act itself, 

 if the female did not embrace the male with the long bristles of 

 her hinder feet, and the male the female with the bristles of his 

 third pair of feet, and at the same time attach himself firmly to 

 the ventral surface of the female with the sucking cups of his last 

 pair of feet. The males never penetrate into the galleries of 

 impregnated, egg-laying females, as is shown by the unbroken 

 series of the eggs. 



Of the duration of the life of the mites in their particular 

 stages of development, Gudden gives the following calculation : 

 The hatching time of the eggs lasts about eight days ; on the 

 seventeenth day after transference hexapod broods in the act of 

 moulting are found, in forty-three days female mites after their 

 last change of skin, and in forty-eight days the first egg-gallery 

 with eggs. We may therefore reckon somewhat in this manner : 

 eight days, hatching time of the eggs ; duration of each change 

 of skin six days, interval between them five days ; which gives as 

 the commencement of the first change of skin about the four- 

 teenth day, of the second the twenty-fifth day, of the third the 

 thirty-sixth day, and of the oviposition the beginning of the 

 seventh week. If the males die soon after copulation, they would 

 attain an age of about six weeks. 



Mode of infection of itch. Gudden first discussed this 

 question rationally in accordance with the desire of wandering at 

 the different periods of life. The most restless are the males 

 seeking after females, and next to these the young ; these, there- 

 fore, are the most easily transferred ; lastly, just fertilised females 

 after the third change of skin, which wander out of their old 

 passages, in order to dig new ones for themselves, in which to 

 lay their eggs. Females already engaged in oviposition, or near 

 it, can rarely, if ever, be the cause of itch, as they never leave 

 their galleries again. It is only in deep-seated itch that these 

 last may perhaps be transferred from one place to another on the 

 body of the same individual. Hebra and Gudden do not coin- 

 cide with the opinion defended by Von Liebig and Bourguignon, 

 that the itch-mites are nocturnal predaceous animals ; they regard 

 the wanderings of the mites as solely arid wholly dependent upon 



