Laws of Licubation and Gestation. 

 Table II. 



273 



la an appendix to this paper I shall give a list of 1 05 birds, for 

 which I have been able to obtain records of the weight and of the 

 incubation period of each. I have, indeed, found records of the 

 weights of over 500 species and incubation periods of an almost 

 equal number ; but in only these 105 cases can both items of 

 information be had for the .same bird. They are sufficient, 

 however, to show that the law enunciated holds good with only 

 one notable exception, the Apteryx, which is wholly isolated if the 

 figures given by Buller are to be accepted. There is one dubious 

 case — the Emu. But in such an enquiry allowance must be made 

 for the want of detiniteuess in the figures. Many observers are 

 content to say that a bird broods for 3 or 4 weeks. Even so 

 lareful a writer as Brehm, gives very many of his incubation 

 periods in the same inaccurate fashion. Nor do the authorities 

 agree well together. For a bird so well-known as the Swan, 

 Brehm gives 48 days as the period ; poultry books say 6 weeks, 

 while Bechstein, a very competent authority, gives 5 weeks. In 

 regard to the ostrich, Anderson gives .38 days, Brehm gives 45 

 to 52, while St. George Mivart says 50 to 60, and half-a-dozen 

 other authorities give various intermediate periods. Tn all such 

 cases I have taken the mean. But there are many, no doubt, 

 not to be accepted as more than very rough appi'oximations. 



