152 



INSECTS CRUSTACEA DIAGRAM 7 



CLASS CRUSTACEA. 



The Crustacea, with the insects, arachnida, and myriapoda, form 

 the great division of articulate animals, that is animals formed of 

 segments. The Crustacea may be easily known by always having 

 more than four pairs of legs ; they have ten, as in the cray-fish and 

 crab, or a much greater number ; the wood-louse, for instance, has 



Crab. 



fourteen. Crustacea, like insects, have lateral jaws, and eyes in 

 which the facets may easily be seen, but they never breathe by 

 tracheae : they have branchia like fish. They undergo frequent 

 moults. 



The Crayfish. In the crayfish the head and thorax are united. 



