26G INSTINCTS OF BIRDS. 



probability, be ascribed to a change in their 

 organization, occasioned by the artificial mode 

 of hfe to which they have been subjected. Now 

 as it is a maxim in physiology, that the exercise 

 of every animal function is dependant upon its 

 appropriate material organ, any display of new 

 instinctive phenomena, in birds which have long 

 been under the controul of man, may also be 

 attributed to the operation of the same physical 

 cause. The singular propensity of the cropper 

 pigeon to inflate its craw with air, and the still 

 more remarkable disposition of the tumbler to 

 turn itself over backwards when on wing, which 

 are permanent characters in- these varieties of 

 of the rock-dove, being transmitted by genera- 

 tion, can be satisfactorily accounted for on the 

 foregoing supposition only. How unsafe it must 

 always be to draw general conclusions from the 

 habits and propensities of domestic fowls alone, 

 whose instincts are frequently changed, almost 

 as much as their plumage, by the unnatural 

 state in which they are kept, needs scarcely to 

 be insisted on. 



Dr. Darwin conjectures that birds learn how 

 to build their nests from observing those in 

 which they are educated, and from their know- 

 ledge of such things as are most agreeable to 

 their touch in respect to warmth, cleanliness. 



