ARTHROPODS. 



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are almost . always separate, the reproductive organs and 

 ducts are paired. There is often some metamorphosis in 

 the course of development. In habit the Arthropods are 

 predominantly active. 



Class Crustacea. 



General Characteristics of Crustaceans (to which primitive, 

 parasitic, and degenerate forms offer exceptions). 



With the exception of the land-crabs, wood-lice, and sand- 

 hoppers, the Crustaceans live in water and breathe by gills, 

 or through the skin. The head carries two pairs of antennae 

 along with other appendages ; the thorax or median part of 

 the body also bears limbs; the posterior region or abdomen is 

 usually segmented, and often furnished with appendages. 

 The typical appfendage consists of two forks and a basal 

 portion to which gills are often attached. To the chitin 

 of the cuticle, carbonate of lime is added. 



There are two sub-classes of Crustaceans : — 



