[The rate at which these Acari breed is very great. Gerlach has found that roughly, in each Sarcopt gallery, a female produces fifteen individuals—ten females and five males—and that the progeny reproduce again in fifteen days. The table given below thus shows that one pair may produce the enormous number of 1,500,000 descendants in three months:—
| First generation after 15 days | 10 | females | 5 | males | |||
| Second | " " 30 " | 100 | " | 50 | " | ||
| Third | " " 45 " | 1,000 | " | 500 | " | ||
| Fourth | " " 60 " | 10,000 | " | 5,000 | " | ||
| Fifth | " " 75 " | 100,000 | " | 50,000 | " | ||
| Sixth | " " 90 " | 1,000,000 | " | 500,000 | " | ||
= 1,500,000 individuals. | |||||||
[These Acarinæ are divided into three distinct sub-families, namely the Cytolichinæ, Sarcoptinæ, Canestriniinæ.
[The Sarcoptinæ alone interest us here, and of the nine genera the three following are the most important:—
[(1) Sarcoptes, Latreille; Eusarcoptes.
[(2) Psoroptes, Gerv.; Dermatodectes, Gerlach; Dermatocoptes, Fürstenberg.
[(3) Chorioptes, Gerv.; Symbiotes, Gerlach; Dermatophagus, Fürst.; Sarco-dermatocedes, Del.
[The following are the main characters of these three genera:—
[Sarcoptes—round or slightly oval; the two posterior pairs of legs being nearly or quite concealed beneath the body; the tarsi end in simple long pedicles, with ambulatory suckers.
[Psoroptes—oval; the legs are all visible outside the margin of the body; the ambulatory suckers are carried on long triangulated stalks; the male has copulatory suckers and abdominal prolongations.