XI PHENOMENA OF ORGANIC NATURE 421 



briefly the different habits of the breeds of 

 Pigeons, all of which depend upon their physio- 

 logical peculiarities as the peculiar habit of 

 tumbling, in the Tumbler the peculiarities of 

 flight, in the " homing " birds the strange habit 

 of spreading out the tail, and walking in a peculiar 

 fashion, in the Fantail and, lastly, the habit of 

 blowing out the gullet, so characteristic of the 

 Pouter. These are all due to physiological modifi- 

 cations, and in all these respects these birds differ 

 as much from each other as any two ordinary 

 species do. 



So with Dogs in their habits and instincts. It 

 is a physiological peculiarity which leads the 

 Greyhound to chase its prey by sight that enables 

 the Beagle to track it by the scent that impels 

 the Terrier to its rat-hunting propensity and 

 that leads the Retriever to its habit of retrieving. 

 These habits and instincts are all the results of 

 physiological differences and peculiarities, which 

 have been developed from a common stock, at 

 least there is every reason to believe so. But it 

 is a most singular circumstance, that while you 

 may run through almost the whole series of 

 physiological processes, without finding a check to 

 your argument, you come at last to a point where 

 you do find a check, and that is in the reproduc- 

 tive processes. For there is a most singular cir- 

 cumstance in respect to natural species at least 

 about some of them and it would be sufficient 



