ZOOLOGY 
The alimentary canal is often provided with salivary 
glands ; the stomach may give off numerous caeca, which in 
iL € A /, 
Fic. 240.—Cheyletus jlabellifer 
(Book Mite, quite unconnected 
with books). 
some cases are forked. The stig- 
mata are two in number, situated 
near the hind pair of legs, the 
tracheae may be long and fine, in- 
terlacing with the viscera, but in 
some species (Nothrus) they are 
short and thick, and in Hoplophora 
they are still shorter and end in 
swollen vesicles. 
As a rule a circulatory system is 
absent, but the GAMASIDAEB, or beetle 
mites, are described as having a two- 
chambered heart with two pairs of 
ostia. 
A coxal gland has been de- 
scribed, but no opening to the exterior has yet been found. 
The nervous system is very concentrated, one or two pairs of 
eyes may be present or these organs may be entirely absent. 
The male and female generative glands are very much alike ; 
as in Phalangids, they form a ring. Their external opening is 
on the anterior end of the abdomen or between the last pair of 
legs. The Acarina are oviparous, the young are hatched with 
three pairs of legs and undergo a num- 
ber of ecdyses. Sphaerogyna ventricosa 
is said to give birth to mature mites 
which are fertilised as soon as. born. 
The Acarina are divided into many 
families, some of which may be men- 
tioned. The DERMATOPHILI comprise 
one genus, Demodex, which is found 
living in hair follicles both in domesti- 
cated animals and in man. It has a 
suctorial rostrum, four pairs of rudi- 
mentary legs, and a long annulated 
abdomen. 
Fic. 241.—Demodex folli- 
culorum, Simon. 
Under side. 
a, Rudimentary legs. 
b. 
Abdomen. 
The SARCOPTIDAE are microscopic mites which live parasitic- 
ally in the skins of mammals, and give rise to diseases known 
