46 PARASITOLOGY. 
Gamasidae and Trombidiidae, to which belong 
species of parasites infesting birds and small ani- 
mals. (The chigger belongs to the latter family. 
Sarcoptidae (Sarco—flesh; kopto—to cut.) This 
sub-family is divided into three important genera, 
producing scabies in allanimals. It includes the air- 
sac mite. 
Demodecidae include the parasites that produce 
follicular or red mange. 
Argasidae and Ixodidae include the ticks. 
In these parasites the divisions of head, thorax and 
abdomen are not distinctly marked, macroscopically. 
They are all blood-suckers. The head is provided 
with a stylet for piercing the skin and sucking the 
blood. The piercing mandibles are surrounded by 
two palpi. The eyes are small or wanting. The 
larva is provided with three pair of legs, the adult 
with four. The free extremity of the last segment 
is provided with a hooklet, ambulacrum or pulvillum, 
which aids the parasite in holding on to its host. 
ACARIASIS. 
This is a condition of an animal being infested 
with some species of parasites belonging to the order 
Acarina. There are two kinds of Acariasis, viz: 
Psoric and non-psoric. 
Psoric Acariasis is a condition in which the para- 
sites produce scab; infested by species of the sub- 
families Sarcoptidae and Demodecidae. 
Non-Psoric Acariasis is a condition in which the 
parasite does not produce scab; infested by species 
of the families Gamasidae, Trombidiidae, Argasidae 
and Ixodidae. 
