Precocity seems to me to be an acquired character of 

 expediency, found in a heterogeneous mixture of species. 

 To many, precocity is synonymous with "lowness," and is 

 said to be a retained reptilian characteristic, the nearer a 

 bird to its proto-reptilian ancestor, the greater its precocity. 

 By this token the low birds should have both long incuba- 

 tion periods and noticeable precocity. However, there are 

 quite a few "low" birds which are the reverse of precocious ; 

 they are definitely altricial, e. g., pelicans, water turkeys 

 and cormorants (65). Pycraft (115) puts the facts much 

 more clearly, and with greater truth, when he says, "When 

 the nestling is active from the moment of hatching, the eggs 

 have a relatively longer incubation period than in cases 

 where the nestlings are for a long time helpless." 



The writer feels justified in holding with Burns (3) 

 that the possession of precocious or altricial characters does 

 not confer thereby long or short incubation periods, and that 

 they are not correlated to the length of incubation as causes 

 to effects. 



Size of Egg 



Glaus (10), Fiirbinger (102), and Chapman (65) all 

 state that the incubation period varies with the size of the 

 egg. Burns (3) says it "seems to depend almost altogether 

 on mere size or bulk" of egg, while Evans (2) in his second 

 conclusion feels willing to hold "that within each group, 

 the larger the egg, the longer the period." 



What is meant by "size of egg" ? It does not seem pos- 

 sible that these (and other) writers mean mere size as ex- 

 pressed by length and breadth, for these two dimensions 

 cannot possibly account for, and produce, the endless varia- 

 tions in the shape of eggs, variations of shape which produce 

 corresponding differences in bulk, nor does it seem possible 

 that they believe the infinity of bulks produced by these dif- 

 ferences in shape would be paralleled by corresponding 

 alterations in the incubation period. If there be any rela- 

 tion between the size of the egg and the duration of its 

 incubation, the writer feels that the term "size" should be 

 taken to mean weight, for after all is said, these differences 

 in measurements and shape result in corresponding varia- 

 tions in egg weight. If all birds' eggs were of the same 

 specific gravity, and if there were a fixed relation between 

 the length-breadth index and the weight, one could easily 

 ascertain the weights of a large number of different birds' 

 eggs, since there is an enormous accumulation of length- 

 breadth measurements at hand, collected with infinite care, 

 toil and patience for years by ornithologists all over the 

 world. Unfortunately I was able to find no data available 

 from which one can learn if all birds' eggs have similar 

 specific gravities, though Spohn and Riddle (173) make 



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