LICE AFFECTING DOMESTIC ANIMALS. 
197 
But very few of the species are ever 
ound upon any other species of animal 
han that which they normally infest, 
tnd if so always upon very nearly re- 
ated species. Whether this is due to 
lifferences in the skin, of temperature, 
>f the size of the hair to which they 
nust adhere and to which their feet 
ire adapted, or to some subtle differ¬ 
ence in the odor or taste peculiar to 
;heir particular host which leads them 
;o discard all others, we are unable to 
Ay. 
The mouth parts are necessarily ca- 
Dable of great extension in order to 
reach the blood of their hosts. Uhler 
says (Standard Nat. Hist., II, p. 209): 
‘A fleshy unjointed rostrum, capable 
d! great extension by being rolled in¬ 
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, ar¬ 
ranged 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.” 
Fig. 1.—Mouth parts of 
Pebiculus veatimenti , show¬ 
ing rostrum and extensile 
tube—greatly enlarged. 
The Sucking Dog-Louse. (Plate I, Fig. 2.) 
Hoematopmus piliferns, Burmeister. 
Although the dog has been the closest companion of man 
among the domestic animals from very early times, and con¬ 
sequently this parasite in all probability was well known to 
