4 THE WORLD OF ANIMAL LIFE 



The Invertebrates are also divided into classes, such as: 

 (i) Molluscs, whose bodies are soft and enclosed in a mem- 

 brane called the " mantle ". 



Some Animals without Backbones 



(2) Insects, which possess six legs and two or four wings, and 

 whose bodies are made up of a number of segments or articula- 

 tions. 



(3) Crustaceans, which are covered with a hard shelly armour: 

 besides other classes. 



The common snail is a good example of the first of these, the 

 butterfly of the second, and the crab of the third. 



We have now seen how animals are grouped, first into divisions, 

 and then into classes. But there is still a great deal to be done, 

 for each of these classes contains a very great number of animals, 

 which cannot all be closely related to one another. We find. 



