DISCUSSION. 429 



depending chiefly on the wide extension of the genus geogra- 

 phically. This illustrates the general type of natural selection, 

 a process by which the fluctuating variations about a mean are 

 taken advantage of in some particular direction in certain locali- 

 ties, with the development therein of races, and finally perhaps 

 of species. What determines these fluctuations, we know not; 

 but it seems natural to suppose, in accordance with observation, 

 that certain conditions of environment will predispose to fluctua- 

 tions in a certain direction, even though these fluctuations be 

 seemingly of little advantage to the individual. Where the 

 connecting links between two groups of individuals, which are 

 developing by fluctuating variations along different lines in 

 separated localities, have disappeared, we have then an instance 

 of Jordan's Law, which is exemplified by the two eastern species 

 of Meliornis and their two western representatives. A similar 

 striking illustration is seen in the eastern and western sj)ecies of 

 Psophodes and Falcunculus. The Australian avifauna would 

 seem, therefore, to furnish examples of the establishment of new 

 species by two quite distinct processes. 



The President summarised the views put forward. The 

 Secretary thanked the Members for their cordial response to 

 the invitation to participate in the discussion. 



