HOW ANIMALS ADAPT THEMSELVES 29 



competition results in the production of sensible 

 novelties, and consequent progress ; but com- 

 petition over-keen results in the production of 

 rubbish, leading to eventual failure. So in the 

 world of animal life ; a certain degree of struggle 

 for existence results in variation, establishment 

 of new varieties, progress. A greater degree 

 results in too rapid variation, new varieties that 

 speedily perish, and finally, the extinction of the 

 type. 



We have spoken of " varieties." Each of the 

 domestic animals presents varieties, which are the 

 cumulative result of the breeder's artificial selec- 

 tion of natural variations. Thus the Pug and the 

 Collie for instance, are varieties of the Dog; the 

 Bantam and the Dorking of the Fowl. Among 

 wild animals, varieties are similarly produced by 

 natural selection, resulting from the " survival of 

 the fittest." By degrees, intermediate forms are 

 lost ; and new species are established by the 

 greater and greater divergence of varieties origi- 

 nally derived from one ancestral type. 



TABLE SHOWING THE POSITION IN CLASSIFICA- 

 TION OF THE ANIMALS NAMED IN THE FORE- 

 GOING CHAPTER 



Phylum MOLLTTSCA, or Shell-fish. 



Class GASTEROPODA, or Snail-like Shell- 

 fish. 



Sub-Glass ANISOPLEURA, or Unequal-sided Gas- 

 teropods. 



Branch STREPTONEURA, or Unequal-sided Gas- 

 teropods with nerves twisted into the 

 shape of a figure of 8. 



