variations in the size of the eggs of the domestic hen and 

 its different races, there is no corresponding variation in the 

 incubation period, be the egg from a bantam or a shanghai ; 

 in other words, the jungle fowl and its bizarre descendants 

 all retain the ancestral length of incubation, viz., twenty-one 

 days. It seems to the writer that if this length were plastic, 

 and altered hand in hand with changes in the size of the 

 egg, it should be strikingly apparent with the domesticated 

 bird, especially the common barnyard fowl, yet, as a matter 

 of fact, there is, to reiterate, not only no change to be noticed, 

 but a tenacious retention of the primitive ancestral duration 

 of incubation. 



Poultrj' raisers (103) have long recognized several dif- 

 ferent factors which produce large variatioiis in the sise of 

 hens' eggs, and these factors have been given by Curtis 

 (140), as follows: Age of hen, season of laying, state of 

 health of hen, position of egg in the egg laying period 

 (i. e., the first or the last egg laid), the rate of egg produc- 

 tion, and lastly the food consumption of the hen. It is 

 possible that some of these factors can have no existence 

 with birds in the wild state, yet, on the other hand, some 

 api3ear to exist with birds in natural conditions, and still 

 seem unaccompanied by parallel changes in the length of 

 incubation. 



If egg size (indicated by measurements) be examined 

 as to its relation to the length of incubation, one finds a 

 complicated condition of affairs. Newton (25) says that 

 the eggs of the guillemot (A. troile) are ten times the size 

 of those of the raven, yet the incubation periods of these 

 birds are but three to one, while the eggs of the eagle (sp?) 

 and those of the guillemot are recorded (25) as being almost 

 the same in size, but there is a difference of four or six days 

 in the lengths of incubation of these two species. The incu- 

 bation periods of the elf owl and of several hummingbirds 

 are similar, yet there is a large difference in the sizes of 

 their respective eggs. The eggs of the flamingo and some 

 megapods are nearly alike in length and breadth, neverthe- 

 less the first incubates twenty-eight days and the second 

 forty-two days, rather than being identical, as would happen 

 were this egg-size control theory correct. 



The above are all examples from species belonging to 

 different families, and as Evans has stated, there is not much 

 relation between egg size and the length of incubation but- 

 side of the boundaries of natural groups (families). There 

 are, however, numerous exceptions also to be found within 

 families. 



The eggs of the white and the brown pelican are recorded 

 as differing noticeably in size, but both species have the 

 same duration of incubation. Furthermore, eggs laid by 



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