98 THE MICROSCOPE, 
results of an extended series of investigations, by which many points 
n the anatomy and life-history of this parasite (which he called 
“ Entozoon folliculorum’’ ) were for the first time clearly demonstra- 
ted. Since then numerous investigators and naturalists, notably 
Mégnin and Gruby, have added largely to our knowledge of the 
morphology of the animal. 
The Acarus folliculorum, Demodex folliculorum, or Steatozoon 
folliculorum, as it has been variously called, is an ecto-parasitic mite 
belonging to the family Vanurides, of which it is the type, of the 
order Acaridea, of which it is one of the lowest forms. 
I have here some photographs showing the animal in different 
positions, taken from Wilson’s work on ‘“‘ Healthy Skin and Hair’; 
and also a photograph showing the cephalo-thorax of the parasite, 
taken from a steel-plate kindly loaned me by vice-president C. C. 
Mellor. This plate makes the finest picture of the portion of the 
mite it represents, that I have ever seen, and is, I am sure, the best ever 
made of this or any other animal of its kind. The photographs were 
made for me by our fellow-member, Mr. W. 8. Bell, and very aecu- 
rately represent the Acarus. 
Under my microscope I have a slide prepared in glycerine, 
showing a specimen of Demoder folliculorum, taken from the skin 
of the nose of a young lady of this city. 
Looked at individually, Acarus folliculorum is a well propor- 
tioned, symetrical little animal, of an average length of about one 
one-hundredth of aninch. The anterior one-third of his length con- 
sists of a cephalo-thorax, along the sides of which are ranged, in the 
mature individual, four pairs of rather rudimentary legs. Like some 
other acaridea, the immature animal has but three pairs of locomotor 
organs. Two movable organs, probably palpi, are set in the ante- 
rior extremity of the cephalo-thorax. To the posterior extremity of 
the cephalo-thorax, which varies but little in length, is joined a long, 
tail-like body which varies very greatly in length. The integument 
is soft, transparent, and striated circumferentially. 
The animal is oviparous; the egg being of a relatively large 
size. 
Let us look for a moment at the habitat of Acarus folliculorum. 
This parasite is found in the unctuous plug cf hardened secretion 
which occupies the ducts of the subaceous folicles of the skin. This 
cheesy plug, which forms the nidus and furnishes the pabulum for 
the little fellow, is produced by a dilation of the follicles, resulting 
from a sluggish, ill-functionating condition of the skin, present, to a 
