the bird's temperature can permanently alter the true length 

 of its incubation period, 



Whence I would suggest the following 



Hypothetical Law, 

 That the true or specific length of incubation is fixed by 

 the "lowness" or "highness" of the species, particularly by 

 the physiologic "lowness" or "highness," both of which are 

 fixed by the distance the species has traveled (without re- 

 treating) from its proto-avian ancestor. 



TABLE NO. 1 



Incubation Periods* 

 \T' Family— Species _ Period Authority 



Struthionidae 



Struthio Camelus — Ostrich 36 to 40 days 1 



Struthio Camelus — Ostrich 45 to 48 days 9 



Struzzo -. 50 to 60 days 12 



Ostrich 50 to 60 days il 



Ostrich 42 to 49 days 10 



Ostrich 42 days 7 



Ostrich 42 days 8 



Ostrich (In incubator) 42 days 6 



Eheidae 



Ehea Americana — Common Rhea 35 days 1 



Ehea Americana — Nandu 39 days 9 



Rhea Americana — Great-billed Rhea 6 weeks 94 



Rhea darwinii — Darwin's Rhea.'. ... .30 to 31 days 13 

 Dromaeidae 



Dromaeus novae-hollandiae — Emu 56 days 1 



Dromaeus novae-hollandiae — Emu . . . about 8 weeks 10 



Dromaeus novae-hollandiae — Emu 58 days 9 



Dromaeus novae-hollandiae — Emu . . . about 8 weeks 14 

 Dromaeus novae-hollandiae — Emu (under 



hen) 7 weeks 17 



Dromaeus novae-hollandiae — Emu (Under . 



normal parents 9 & S) 57 days 17 



Dromaeus novae-hollandiae — Emu (Under 



normal parents 9 only _ ... 63 days 17 



Emu 50 days , 15 



Emu 58 days 94 



Dromaeidae "the period being 80 days" 16 



Dromaeidae 70 to 80 days 25 



Casuariidae 



Casuarius bennetti — New Britain Casso- 

 wary — (Mooruk) 42 days 1 



*The author is confident that some of the incubation- length records 

 included in this list are grossly incorrect, ycrf; they are incorporated in 

 the data, with a feeling that they will, in the future, be more accu- 

 rately determined, and in that form recorded, and thus be corrected. 



77 



