'CHAPTER XII 
HOMINOXIOUS ARTHROPODS 
The following synoptic tables are presented in the hope that they 
may be of service in giving the reader a perspective of the relation¬ 
ships of the Arthropoda in general and enabling him to identify the 
more important species which have been found noxious to man. 
Though applicable chiefly to the arthropods found in the United 
States, exotic genera and species which are concerned in the trans¬ 
mission of disease are also included. For this reason the keys to the 
genera of the Muscids of the world are given. As will be seen, the 
tables embrace a number of groups of species which are not injurious. 
This was found necessary in order that the student might not be 
lead to an erroneous determination which would result were he to 
attempt to identify a species which heretofore had not been considered 
noxious, by means of a key containing only the noxious forms. The 
names printed in bold faced type indicate the hominoxious arthropods 
which have been most commonly mentioned in literature. 
CRUSTACEA 
Arthropods having two pairs of antennae which are sometimes 
modified for grasping, and usually with more than five pairs of legs. 
With but few exceptions they are aquatic creatures. Representatives 
are: Crabs, lobsters, shrimps, crayfish, water-fleas, and woodlice. 
To this class belongs the Cyclops (fig. 122) a genus of minute aquatic 
crustaceans of which at least one species harbors Dracunculus medi- 
nensis, the Guinea worm (fig. 121). 
MYRIAPODA 
Elongate, usually vermiform, wingless, terrestrial creatures having 
one pair of antennas, legs attached to each of the many intermediate 
body segments. This group is divided into two sections, now usually 
given class rank: the Diplopoda or millipeds (fig. 13), commonly 
known as thousand legs, characterized by having two pairs of legs 
attached to each intermediate body segment, and the Chilopoda 
or centipeds (fig. 14) having only one pair of legs to each body seg¬ 
ment. 
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