ARTHROPODS. 



FlG. 9. — Cephalopod (paper nautilus, female), 



The nervous system has three chief pairs of nerve centres 

 or ganglia. In many cases the larval stages are very 

 characteristic. 

 Arthropods. — This large series includes Crustaceans 



Fig. 10. — Fresh-water crayfish 

 (Astacus), a Crustacean. — 

 After Huxley. 



Fig. 11. — a, Caterpillar ; b, 

 pupa ; c, butterfly. 



