90 Mr. W. Evans on the Periods 



The Pygopodes, particularly tlie Alcidae, which lay a single 

 large egg, sit for a lengthened period — 30 to 33 days in the 

 case of the Common Guillemot and Razorbill, and even 

 more in the case of the PufiBn, unless the egg hatched in my 

 incubator took an abnormally long time. 



I have only seen two statements regarding the period among 

 the Impennes^ namely, Sir Wy ville Thomson's, that the Tufted 

 Penguin takes about 6 weeks; and that of Prof. Studer, 

 which Dr. Gadow looks upon as an under-estimate. 



A solitary instance exhausts my information concerning the 

 Cryptwi. According to Mr. Bartlett, the Rufous Tinamou 

 hatched its eggs in the Zoological Society's Gardens in 21 days, 

 which is about the same time as the typical Gallince take. 



The Casuarii are a very long-period race, longer relatively 

 than the Struihiones — the Emu, for instance, requiring about 

 2 months' incubation, the Rhea taking from 1 to 2 weeks 

 less ; but the time seems very elastic in these two Orders. 

 It would appear that by artificial incubation Ostrich eggs 

 may be hatched in from 40 to 45 days, whereas in the natural 

 state they take fron 55 to 60 days. 



Unfortunately I am unable to cite a reliable record of 

 the period of incubation among the Apteryges. That it is 

 of long duration may be inferred from the fact that an 

 Apteryx in the Zoological Gardens, London, sat on an egg 

 the unprecedented time of within a few days of 4 months, the 

 egg, however, proving unfertile (Bartlett, P. Z. S. 1868, 

 p. 329). 



To sum up : while in a broad sense it may be said that 

 the larger the egg the longer the period of incubation, it is 

 evident that such a rule cannot be applied with any certainty 

 unless the eggs compared belong to birds possessing a con- 

 siderable amount of affinity. Consequently, before we ven- 

 ture to predict of any two eggs, not very dissimilar in size, 

 that the one will have a shorter period than the other, we 

 must take into consideration the Order, or perhaps even 

 the Family, to which each belongs, as well as their relative 

 size. If size alone were relied on, we should conclude, for 

 instance, that a Partridge's egg would hatch in less time than 



