408 The Bell-birds of America. 



upon the individuals located in each of these four .separate 

 areas in a different manner, according to the different natural 

 influences (such as food, weather, climate, etc.) affecting them. 

 Communication being cut off between them, there would be no 

 neutralization of the variation occurring in one area by a con- 

 trary variation occurring in the adjoining area. The four isolated 

 colonies of our G. priscus would therefore, in process of time, 

 become a series of four distinct species, as represented in Fig. 4. 



It will be remarked in the present case that the variation 

 which has taken place has mainly affected the male birds. 

 The females of the four species of Ghasmorhynchus are still 

 nearly identical. There has been manifestly a much greater 

 " struggle for existence," as Mr. Darwin calls it, amongst the 

 males than amongst the females of these birds. And it is not 

 difficult to see how this has occurred. The very object of the 

 structures that have altered in the present instance is to render 

 the male agreeable to its mate, so that we have here an influ- 

 ence that would work forcibly upon the male sex, and cause 

 it to vary, while it would leave the female untouched. 



It appears, therefore, that if we adopt Mr. Darwin's theory, 

 a few simple hypotheses will enable us to give a reasonable 

 explanation of the mode in which the present distribution of 

 the four species of the Bell-bird may have been brought about. 

 Similar hypotheses will explain hundreds and thousands of 

 other cases in which groups of animals and plants offer corre- 

 sponding phenomena as to their geographical distribution. 

 What the exact influences were that divided up the area for- 

 merly occupied by the common progenitor of the four Ghas- 

 morhynchi, it would be impossible at present to say ; but it 

 will be seen at once that when the geological structure of the 

 earth is more perfectly known, great light will nedbssarily be 

 thrown on problems of this nature. Such problems, in our 

 present state of ignorance of the formation of the greater part 

 of the earth's surface, it would be vain to attempt to answer 

 in a decisive way. But it seems better, even under present 

 circumstances, to attempt some sort of explanation of these 

 and similar phenomena, than to remain content with the deus- 

 ex-machind theory of " special creation/' which is in fact no 

 theory at all, but only a periphrastic way of confessing our 

 ignorance of the subject. 



