ARTHROPODS. CLASS CRUSTACEA lil 
109. Peripatus (class Onychophora),—It is generally be- 
lieved that the Crustacea, insects, and spiders, together 
with their numerous relatives, trace their ancestry back to 
animals that bore a certain resemblance to the segmented 
worms. Most of these ancient types have 
long been extinct, but here and there 
throughout the earth we occasionally meet 
with them. 
Among the most interesting of these 
are a few widely distributed species belong- 
ing to the genus Peripatus (Fig. 66), but as 
they are comparatively rare we shall dis- 
miss them with a very brief description. 
They usually dwell in warm countries, un- 
der rocks and decaying wood, emerging at 
night to feed on insects, which they ensnare 
in the slime thrown out from the under 
surface of the head. Their external form, 
their excretory system, and various other 
organs are worm-like. On the other hand, 
the appendages are jointed, and one pair 
has been modified into jaws. The peculiar 
breathing organs characteristic of the in- 
sects are also present. Peripatus therefore 
gives us an interesting link between the 
worms and insects, and also affords an idea 
of the primitive insects from which the 
modern forms have descended. 
110. The centipeds and millipeds (class Src etre 
Myriapoda).—Many of the myriapods—that (peripatus anita 
is, the centipeds and thousand-legged worms — Twice the natural 
—are familiar objects under logs and stones“ 
throughout the United States. The first of these (Fig. 67) 
are active, savage creatures, devouring numbers of small 
animals, which they sting by means of poison-spines on the 
tips of the first pair of legs. .The bite of the larger tropical 
