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EXOSKELETON 



FIG. 9. Vertical section of shell or'exoskeleton. 



The epidermis thrusts off successive layers of its substance, which form a number of delicate 

 laminoe superimposed upon one another, and this is impregnated with salts of lime. The 

 exoskeleton thus formed is cuticular, to be distinguished from cornified epidermis, as nails, 

 composed of modified cells, a cellular exoskeleton. 

 CLASSIFICATION 



Sub-Kingdom Arthro'poda (Gr. arthron, a joint; pous, a foot). The body is segmented; 

 limbs jointed ; nervous system forms a ring round gullet, followed by a ventral chain of 

 ganglia. 

 Natural Order Crustacea (L. crusta, a crust), because it breathes by gills ; has two pair of 



antennae (lesser and greater) ; walking legs borne by thorax and abdomen. 

 Genera Homarus, Astacus. 

 Common Names Lobster, Crayfish. 



