CHAPTER XIX. 

 THE ARACHNOIDS. 



CLASSIFICATION OF THE ARACIINOIDEA. 



Order. 



Acarina 



Family. 



Trombidiidae 

 Gamasidae 



Tyroglyphidae 

 Sarcoptidas 

 DemodicidcTg 

 Tarsonemidae 



Subfamily. 



Ixodidae 



Argasinae 



Ixodinae 



Linguatulida 



The class Arachnoidea and the class Insecta belong to the phylum 

 Arthropoda. This phylum contains a greater number of species than 

 does any other phylum. 



While the lobsters, crabs and water fleas, which belong to the class 

 Crustacea, are important zoologically, they are of very slight impor- 

 tance medically. Besides the Crustacea we have the thousand-legged 

 worms or Myriapoda. 



The different classes of Arthropoda resemble the segmented worms 

 but have as distinction the possession of jointed appendages which 

 proceed from the somites in pairs. Some of the pairs of limbs are for 

 locomotion; at times, certain ones may be specialized for food taking. 



The somites or divisions of the body have a chitinous exoskeleton. 



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