CREATION BY LAW. 235 



an identity in physical characters must be due. 

 This identity prevails not only in such essential 

 matters as the structure of the bill and tongue, in 

 the form of the feet and of the wings, in the habits 

 of flight, in the nature of the food, but runs also 

 into some very curious details, as, for example, in 

 the number of feathers in the tail and in the 

 wings, which are constant numbers — adhered to 

 even when some of the feathers, not being used 

 even for ornament, are reduced almost to rudi- 

 ments. But under degrees of development which 

 are very variable, the number is invariable. This 

 identity of structure is the more remarkable from 

 the immense extent of the group which it charac- 

 terises. There are now known to science no less 

 than about 430 different species of Humming 

 Bird ; and it cannot be doubted that many more 

 remain to be discovered among the immense forests 

 and mountain ranges of Central America. 



Now, what is the bond that unites so closely, in 

 a common structure, all the forms of this great 

 Family of birds ? We think it a sufficient explana- 

 tion sometimes of the likeness of things, that they 

 are made for a common purpose. And so it is 



