196 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
Mange- or Itch-Mites exhibit degrees in parasitism. Some 
of them (Dermatophagus) simply devour the loose scales which 
are constantly being detached from the epidermis, while others 
(Dermatocoptes) suck blood. But the most objectionable (Sav- 
Fig. 1142.—a, Root of hair; (2) enlarged, showing a 
coptes, fig. 1142), those respon- 
sible for the unpleasant disease 
known as “itch”, actually bur- 
row in the skin, within which the 
female lays her eggs, and may 
therefore be described as true 
internal parasites. They live on 
the blood and other juices of 
their hosts. 
A curious little elongated mite 
(Szmonea folliculorum, fig. 1142) 
lives in the little bag-like glands 
attached to the roots of hair, in 
which a sort of fatty matter is 
swollen sebaceous gland (4), containing a Hair-Mite secr 
(Simonea folliculorum). 8, A Hair-Mite, greatly en- ec eted. 
larged. c, An Itch-Mite Sarcoptes scabet), greatly The degenerate Tongue 2 
enlarged. 
Worms (Lznxguatulida), which 
live in the noses ot dogs and wolves, are doubtfully classed with 
the Arachnida (see vol. i, p. 393). 
CRUSTACEANS (Crustacea) AS PARASITES 
A large number of the lower Crustaceans are parasitic, and 
Fig. 1143.—A Carp-“‘ Louse” 
(Argulus), enlarged 
some of them have become extremely de- 
generate as the result of their mode of life, 
especially in the case of the females. A 
few examples must suffice. 
ForkK-FOoTED Crustacea (CopEPoDA) 
Aas Parasires.—Many of the members of 
this group are found attached to fishes, 
usually by means of their suctorial mouths. 
They are popularly, though somewhat in- 
appropriately, known as Fish -‘ Lice”. 
Among the least modified kinds are those 
(Argulus, fig. 1143) found attached to the 
skins of carp and sticklebacks, holding on by a couple of suckers 
