PARASITES AFFECTING THE SKIN 9 
twenty-four oval-shaped eggs in one batch, each con- 
taining an embryo, just visible when examined micro- 
scopically. About a month after the completion of this 
function the female dies. Ina week each egg hatches out 
a larva, which possesses only six legs, and hence is termed 
the “ hexapod larva.” It possesses no sexual organs. 
In its turn the larva becomes a nymph, with eight 
legs, but is still asexual: but in a few more days it 
develops generative organs, and becomes a sexually 
adult parasite. The whole process, from the egg stage 
to the adult, takes about three weeks. 
The males crawl about, and each, after fertilizing 
a number of females, dies in about six weeks. The 
mange parasites can exist away from any animal host 
for a period of from two weeks to two months. 
Rugs and grooming implements remain infective for 
three weeks or longer, but on damp walls and partitions 
the parasites may remain active for two months. In 
warm surroundings and in sunlight they become more 
active. 
There are four chief varieties of mange parasites, viz. : 
Sarcoptes, producing sarcoptic mange ; Psoroptes, pro- 
ducing psoroptic mange ; Symbiotes, sometimes known 
as Chorioptes, producing symbiotic or chorioptic mange ; 
and Demodecide, producing follicular or demodectic 
mange. 
1. Sarcoptes.—These are the smallest of the mange 
parasites, and are burrowers—that is, they live beneath 
the surface of the skin in tunnels, which they bore out. 
They usually reach the rete Malpighii, where they live 
on lymph. 
The body is rounded, as is also the rostrum. The 
legs are short, and bear simple unsegmented long 
pedicles. These are absent in the third pair in the 
male, and in the third and fourth pairs in the female. 
The posterior two pairs of legs are ventrally placed and 
