DISTRIBUTION. 



43 



matter, except in so far as each uses, or may use, his utmost 

 exertions to secure that the choice of the female may fall upon 

 him. The circumstances supposed to influence, and ulti- 

 mately determine, the choice of the female, are of course, in 

 the main, the personal attractions of some particular male, the 

 female being captivated by some "beauty of form, colour, 

 odour, or voice," which such a male may possess. 



If it be admitted that the females of some of the lower 

 animals have the power of expressing and exercising a pre- 

 ference in the manner above indicated, then it is easy to 

 understand how variations might be transmitted or intensi- 

 fied in this way. The male who is most attractive to the 

 female will, other things being equal, have the best chance 

 of propagating his species, and is likely to leave the largest 

 number of descendants. His male offspring will inherit the 

 peculiarities by which their sire was rendered pre-eminently 

 attractive in the eyes of their mother, and thus a well-marked 

 breed might be produced, by the preservation or intensifica- 

 tion of characters of this nature. Mr Darwin is disposed to 

 believe that colour and song in most, if not in all, animals are 

 thus to be ascribed to the action of Sexual Selection, through 

 numerous successive generations ; but other competent autho- 

 rities are unable to concur in this view. 



14. DISTRIBUTION. 



Under this head come all the facts which are concerned with 

 the external or objective relations of animals that is to say, 

 their relations to the external conditions in which they are 

 placed. 



The geographical distribution of animals is concerned with 

 the determination of the areas within which every species of 

 animal is at the present day confined. Some species are found 

 almost everywhere, when they are said to be " cosmopolitan ; " 

 but, as a rule, each species is confined to a limited and definite 

 area. Not only are species limited in their distribution, but it 

 is possible to divide the globe into a certain number of geo- 

 graphical regions or u zoological provinces," each of which is 

 characterised by the occurrence in it of certain associated forms 

 of animal life. It is to be remembered, however, that the 

 zoological provinces of the present day by no means corre- 

 spond with those of former periods, and that they have only 

 existed as such since comparatively recent times. 



The vertical or bathymetrical distribution of animals relates 

 to the limits of depth within which each marine species of 



