394 



ESSENTIALS OF ZOOLOGY 



Section I, Branchiata (bran ki a' ta, gill) gill-breathing, aquatic 

 forms for the most part. 



Class I. Crustacea, crayfish, crab, pill bug, barnacle, water flea, 

 etc. 



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Section II. Tracheata (tra ke a' ta, rough) both terrestrial and 

 aquatic arthropods which breathe by tracheae, book lungs or book 

 gills. This section is divided into three divisions depending on the 

 primitiveness of the characteristics. 



