INSECTS IN RELATION TO OTHER ANIMALS 297; 
inoculating them with a protozoan blood-parasite, to the effects 
of which, fortunately, man 1s not susceptible. 
Parasitic Insects.—Insects belonging to several diverse 
orders have become peculiarly modified to exist as parasites 
either upon or within the bodies of birds or mammals. 
Almost all birds are infested by Mallophaga, or bird lice, of 
which Kellogg has catalogued 264 species from 257 species of 
North American birds. Sometimes a species of Mallophaga is 
restricted to a single species of bird, though in the majority of 
cases this is not so. Several mallophagan species often infest 
a single bird; thus nine species occur on the hen, and no less 
than twelve species, representing five genera, on the American 
coot. These parasites spread by contact from male to female, 
from old to young, and from one bird to another when the 
birds are gregarious. When a single species of bird louse 
occurs on two or more hosts, these are almost always closely 
allied, and Kellogg has suggested the interesting possibility 
that such a species has persisted unchanged from a host which 
was the common ancestor of the two or more present hosts. 
Mallophaga are not altogether limited to birds, however, for 
they may be found on cattle, horses, cats, dogs, and some other 
mammals; Kellogg records eighteen species from fifteen 
species of mammals. These biting lice feed, not upon blood, 
but upon epidermal cells and portions of feathers or hairs. 
They have flat tough bodies (Fig. 17), with no traces of wings, 
and a large head with only simple eyes; the eggs are glued to 
feathers or hairs. 
Mammals only are infested by the sucking lice, or Pediculidze 
(Hemiptera). These (Fig. 23) have a large oval or rounded 
abdomen, no wings, a small head, minute simple eyes or none, 
and claws that are adapted to clutch hairs; the eggs are glued 
to hairs. Sucking lice affect horses, cattle, sheep, dogs, mon- 
keys, seals, elephants, etc., and man is parasitized by three 
species, namely, the head louse (Pediculus capitis), the body 
louse (Pediculus vestimenti), and the crab louse (Phthirius 
pubis), though the first two are possibly the same species. 
