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 habiL 

 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 



