Classification and Distribution of Animals. 1 3 



composed of parts similar to those of the neighbouring 

 segments. Such parts are said to be serial homologues, 

 for example the fore and hinder limbs of quadrupeds. 

 These homologies may be complete or incomplete. 



Mimicry. Animals of definite geographical areas 

 often resemble each other in some respects ; thus they 

 may be similar in colour, mostly white, or spotted, 

 or striped, or brightly coloured. Sometimes animals 

 mimic in shape or colour the leaves and twigs on 

 which they live (fig. 6), or the prevalent colour of the 

 herbage. Thus the Kakapo or ground parrot of New 

 Zealand, which can hardly fly, is like in plumage to 

 the mottled green vegetation among which it lives. 

 The ptarmigan and other birds become white in win- 

 ter, and are thus inconspicuous among the snow. 

 Sometimes an insect mimics in appearance another of 

 different nature living in the same district. In such 

 cases the insect imitated is one which, from its dis- 

 agreeable secretions or sting, is not a favourite prey 

 of insect-eaters ; hence the mimicry protects the imi- 

 tator, who is usually rarer than the insect imitated. 



CHAPTER III. 



CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 



Sub-Kingdoms. The animal kingdom includes eight 

 sub-kingdoms. In these we observe a certain pro- 

 gressive increase in complexity, from one end of the 

 series to the other ; but they do not make a linear 

 series, as the highest organism of each is in no degree 

 related to the lowest organism of the next sub- kingdom, 

 being usually much more advanced and specialised, so 



