188 ANIMAL LIFE 
other parts of fish, and derive all their nutriment from the 
body of the fish, show various degrees of degeneration. With 
“some of these fish-lice the female, 
which looks like a puffed-out worm, 
is attached to the fish or other aquatic 
animal, while the male, which is per- 
haps only a tenth of the size of the 
female, is permanently attached to 
the female, living parasitically on her. 
100. Parasitic insects. — Among 
the insects there are many kinds 
that live parasitically for part of 
their life, and not a few that live as 
en ver parasites for their whole life. The 
ca" true sucking lice (Fig. 113) and the 
bird-lice (Fig. 114) live for their whole lives as external 
parasites on the bodies of their host, but they are not 
fixed—that is, they retain 
their legs and power of loco- 
motion, although they have 
lost their wings through de- 
generation. The eggs of the 
lice are deposited on the hair 
of the mammal or bird that 
Fie. 118.—Sucking louse (Pediculus) of 
human body. Fig. 114.—Bird louse (Lipeurus densus).’ 
serves as host; the young hatch and immediately begin to 
live as parasites, either sucking the blood or feeding on the 
