side out, this action serving to bring forward a chaplet of barbs which 
imbed themselves in the skin to give a firm hold for the penetrating 
bristles, arranged as chitinous strips in a long, slender, flexible tube, 
terminated by four very minute lobes, which probe to the capillary vessels 
of a sweat pore (see Fig. 1). The blood being once reached a current is 
maintained by the pulsations of the pumping ventricle and the peristaltic 
movements of the stomach." 
The species infesting man are so nearly related to the others that we 
can not well pass them by without notice. 
THE CRAB LOUSE. 
(Phthirkis inguinalis Leach.) 
If we may depend upon ancient writers this species has been a long 
companion of man. According to Denny it is recorded by Herodotus, 
and according to Piaget was referred to in the writings of Aristotle. 
Some of the ancient accounts treat of it as occurring in the most pro- 
digious numbers and causing most serious ailments to the infested 
parties. The disease produced gained the name of Phthiriasis, though 
doubtless this term has been applied also to the attacks of the other 
species of parasites infesting man. 
Its attacks are said to be more severe than those of the other forms 
of lice, though it is quite probable that in the worst cases reported the 
different species have been present, since the conditions favoring the 
increase of one will favor also the others. The reports, especially of 
the earlier writers, have many of them doubtless been subject to great 
exaggeration, for while the normal rate of increase will account for the 
sudden appearance and rapid multiplication of the lice under certain 
conditions, it is not equal to the marvelous stories which are to be met 
with even in some works that lay claim to accuracy. 
The crab louse infests particularly the 
pubic regious, but occurs also among the 
stiff hairs under the arms, in the beard, and 
it is said also among the hairs of the eye- 
brows. It does not live in the fine hair of 
the head. 
It is very distinct from the other species, 
the body being nearly as wide as long, 
while the strong legs spreading out later- 
ally very greatly increase its apparent 
width and gives it the form of a crab in min- 
iature, thus winning for it the name of crab louse. It is of a whitish 
color, with a dusky patch on each shoulder, and with the legs slightly 
tinged with reddish, the claws having this color more pronounced. It 
is nearly one-tenth of an inch in length. 
Fig. 2. Phthirius inguinalis 
(After Denny from Murray). 
