[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 foimd 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 tjrpe 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, crajrfish, 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 antennae, 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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