8 The Study of Animal Life PART i 



and water-snails, fishes and newts, the dipper and the king- 

 fisher, the otter and the vole. 



As we review the series of animals from the simplest 

 upwards, we find a gradual increase in the number of 

 those which live on land. The lowest animals are mostly 

 aquatic the sponges and stinging-animals wholly so ; 

 worm-like forms which are truly terrestrial are few com- 

 pared with those in water ; the members of the starfish 

 group are wholly marine ; among crustaceans, the wood- 

 lice, the land-crabs, and a few dwellers on the land, are 

 in a small minority ; among centipedes, insects, and spiders 

 the aquatic forms are quite exceptional ; and while the great 

 majority of molluscs live in water, the terrestrial snails and 

 slugs are legion. In the series of backboned animals, 

 again, the lowest forms are wholly aquatic ; an occasional 

 fish like the climbing- perch is able to live for a time 

 ashore ; the mud-fish, which can survive being brought from 

 Africa to Europe within its dry "nest" of mud, has learned 

 to breathe in air as well as in water ; the amphibians really 

 mark the transition from water to dry land, and usually 

 rehearse the story in each individual life as they grow from 

 fish -like tadpoles into frog- or newt -like adults. Among 

 reptiles, however, begins that possession of the earth, which 

 in mammals is established and secure. As insects among 

 the backboneless, so birds among the backboned, possess the 

 air, achieving in perfection what flying fish, swooping tree- 

 frogs and lizards, and above all the ancient and extinct 

 flying reptiles, have reached towards. Interesting, too, are 

 the exceptions ostriches and penguins, whales and bats, the 

 various animals which have become burrowers, the dwellers 

 in caves, and the thievish parasites. 



But it is enough to emphasise the fact of a general ascent 

 from sea to shore, from shore to dry land, and eventually 

 into the air, and the fact that the haunts and homes of animals 

 are not less varied than the pitch of their life. 



3. Wealth of Form. As our observations accumulate, 

 the desire for order asserts itself, and we should at first 

 classify for ourselves, like the savage before us, allowing 

 similar impressions to draw together into groups, such as 



