it is easiest to handle the idea at the same time with altricial 

 conditions of the young. 



Precocity and altricial characters are antipodal, and if 

 precocity confers (or engenders) a long incubation period, 

 it seems reasonable to expect that an altricial species should 

 have a short period. This expectation is realized in a num- 

 ber of instances, the ostrich and the English sparrow being 

 good examples. There are, however, many striking excep- 

 tions; tlie domestic hen and many parrots have identical 

 incubation periods; one is typically precocious and the other 

 is highly altricial; and yet under this explanation the first 

 should have a long period and the second a shorter one. 

 Most, if not all, of the Charadriidae are precocious, which 

 ought to bring about with these species uniformly long incu- 

 bation periods, yet the records clearly show a great variety 

 of lengths of incubation with this family, just about as one 

 would find it in any other fairly large and diversified 

 natural group, /. e., from sixteen to thirty days. Burns (3) 

 justly calls attention to the lack of definite relation between 

 precocity and long incubations, and altricial characters and 

 short incubations, comparing with this in mind, ducks and 

 large hawks, chats and sandpipers, tropic birds and gulls, 

 all examples which in his belief disprove the correctness of 

 the suggestion of a causal relation between precocious and 

 altricial characters and the duration of incubation. If 

 precociousness engendered long incubation periods, a 

 majority of the so-called precoces should have this 

 type of incubation length. Now, if one examine the 

 records of the lengths of incubation amongst the pre- 

 cocious Ratitae, Crypturidae, Phasianidae, Anatidae and 

 others, one finds the incubation length varying from 

 fourteen to fifty-eight days. In other words, with the so- 

 called precoces one finds a wide range of variation in the 

 length of incubation, just as one would find with almost any 

 other group of orders and families indiscriminately mixed 

 together. The supposed correlation of precocity and long 

 incubation may have arisen through a belief that the pre- 

 cocious birds laid large eggs, and that large eggs presuppose 

 long incubations, but large eggs are by no means the rule 

 with the prococes, as is witnessed with the quail, hen, 

 grouse, etc. Furthermore, this does not help this assumed 

 explanation since, it will be shown later, the length of in- 

 cubation is not closely correlated to the size of the egg. 



More or less relevant to this phase of our problem is 

 Gadow's (150) belief that there is a direct relation between 

 the length of incubation and the nesting period. He assumes 

 that the developmental period is made of two portions, 

 embi-yonic and post-embryonic, and that the nest period 

 covers the post-embryonic developmental stage, which is by 



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