60 INTRODUCTION. 



considerable variations having been observed in them when 

 opportunities have been taken, or have occurred, for such 

 notice. 



It appears that, when Turkies have sat on the eggs of 

 the Hen, the duration has been from seventeen to twenty- 

 seven days ; the same bird on its own eggs from twenty- 

 six to twenty-nine days. Hens sat on Ducks' eggs from 

 twenty- six to thirty-four days; on their own eggs from 

 nineteen to twenty-four days. Ducks have sat from 

 twenty-eight to thirty-two days. Geese from twenty-nine 

 to thirty-three days. Pigeons from seventeen to twenty 

 days. It is extremely probable that extended observation 

 will shew still greater irregularities in the various periods 

 of the Incubation of Birds, which seem to increase in du- 

 ration in proportion to the size of the bird : while the 

 Ostrich and Swan require six weeks, and the solitary Dodo, 

 it is said, seven, to complete the process, the Humming-bird 

 takes only about twelve days. 



There can be little doubt that an equability of warmth is 

 one of the essentials in the due process of incubation. 

 Where the Hen frequently leaves her nest and the eggs ex- 

 posed, or where the nest itself is in an unsheltered situation, 

 the process is very often retarded, sometimes, indeed, ren- 

 dered wholly unproductive. Young mothers are generally 

 worse managers of their eggs and their young than those 

 who have had more experience ; in this not differing from 

 the human subject ! 



Although the number of eggs which both domestic and 

 wild birds lay before they are diposed to sit upon them, 

 provided they are not disturbed, is generally pretty regular, 

 yet that number may be considerably increased by removing 

 the eggs as they are laid, leaving one or more in the nest. 

 In domestic fowls this has been so well ascertained, that a 



