no means a safe assumption, since many altricial birds, and 

 practically all the j^rococes, continue post-embryonic de- 

 velopment for a good while after leaving the nest. 



Gadow's conclusion is that a long nest period is pre- 

 ceded by a short incubation period and (inferentially) vice 

 versa. 



While the incubation and nesting periods of some birds 

 support this view, there is also much evidence against it. 

 The screamer and the noddy tern do not bear support to 

 the idea. The secretary bird is reported to incubate forty- 

 two days, yet its young do not leave the nest for six months 

 after hatching (138), and the condor incubates fifty-six 

 days, while its young are reported to live sca en months in 

 the nest after being hatched (154). This question can be 

 examined in another way by making a ratio of incubation 

 length and nest life, counting the latter with precocious 

 birds as zero. The following list gives this ratio with a 

 few species : Domestic hen, 21 ;0 ; house-finch, 14 ;14 ; sparrow 

 hawk, 29;29; golden eagle, 30;35; yellow-headed tropic bird, 

 28;62. It seems to me that while there is much color of truth 

 in this suggestion made by Gadow, whose eminence in zoo- 

 logic work compels attention to his ideas, there is so much 

 against the theory that judgment must still be withheld on 

 its finality. 



Under the second way of putting the explanation 

 comes Arrigoni's (12) statement, which voices also that 

 of Newton (25), Evans (1-2), and Glaus (10). Arrigoni 

 writes: "The period of incubation varies, and is in relation 

 with the state of perfection in which the young are born." 

 It is true that the young of the precoces are physiologically 

 more perfect than are the young of altricial birds, but both 

 are far from being morphologically perfect, and all have a 

 long way to go before becoming so. An English sparrow's 

 nestling is typically the opposite of precocious, yet it hatches 

 out in fourteen days, and s]3ends but fourteen days in the 

 nest. I doubt if a young killdeer reaches an equal level of 

 development in fourteen days after hatching. As a matter 

 of fact, it takes three weeks (after hatching) for young kill- 

 deers to reach a stage of growth permitting them to follow 

 the parents on the wing; it is ten days (after hatching) 

 before they are able to lift their bodies off the ground with 

 their wings alone (183). 



The only birds known to the writer whose young are 

 hatched in a condition approaching "perfection" are the 

 megapodes, and, the writer hopes to show later on, the length 

 of incubation with these birds is not correlated with the state 

 of perfection at hatching alone, but rather with quite an- 

 other characteristic. 



29 



