statements which seem to indicate that the specific gravities 

 of eggs from differing species are dissimilar; and unfortu- 

 nately, also, the length-breadth index bears no relation to 

 the egg weight (140). The writer studied this question for 

 some time, seeking to evolve a formula whence one could get 

 the egg weight from its length-breadth index, but found it 

 impossible of achievement, in which finding he is supported 

 by Curtis (140), who says, "The shape of the egg (hen's), 

 as measured by the length-breadth index, is negatively cor- 

 related with the weight of the egg and with the weight of 

 each of the egg parts." 



It therefore seems to me that the only datum to be used 

 in considering this phase of the problem in hand is, perforce, 

 the weight of the fresh egg, and ,the relation of the egg 

 weight to the length of incubation will be taken up a little 

 later on in this section, while it will be expedient now to 

 consider, more or less carefully, the relation of mere bigness 

 to the incubation length. 



It is quite apparent, after a careful review of the facts, 

 that there is a loose relation between the size of the bird 

 and its egg ; the smaller the bird, the smaller the egg, glaring 

 exceptions noted. This parallelism is more noticeable within 

 the confines of natural groups (families), and within these 

 groups there is also a loose relation between the size of the 

 egg and the duration of incubation, i..e., the larger the egg 

 (and the bird), the longer the incubation, a relation well 

 illustrated by the Buteonidae. There are, however, families 

 wherein this relation does not hold good, or wherein the 

 exceptions are too noticeable to be disregarded. Thus the 

 egg of the guinea hen is decidedly smaller than that of the 

 domestic hen (51) , yet the guinea hen has the longer incuba- 

 tion period ; on the other hand an example is found, in the 

 same family, where the larger egg is accompanied by the 

 longer incubation period, i. e., with the Mikado pheasant as 

 compared with other pheasants. There is, relatively, an 

 enormous variation in the sizes of the eggs of fringilline 

 birds, but the great majority of this family conform more 

 or less closely to the fourteen-day period. There are so 

 many contradicting facts in relation to this theory that one 

 seems impelled to believe that egg size is not a factor in 

 determining the true length of incubation; the size of eggs 

 varies often to a great degree in a single set, and eggs in 

 different sets from individuals of one species differ much in 

 size; the average measurements of eggs from the same 

 species in different regions vary, i. e., those of the Mikado 

 pheasant (68). Nevertheless, all these variations are un- 

 accompanied by corresponding differences in the lengths of 

 incubation. A fact of great weight in this discussion of egg 

 size and incubation is that, notwithstanding the remarkable 



31 



