The optimum incubation temperatures of birds' and rep- 

 tiles' eggs, 



Bird temperatures, 



Temperatures under the incubating bird. 



Reptile temperatures, 



Minutiae of bird physiology. 



Conclusions 



While final judgment and decision must be suspended 

 on many, if not all, of the points at issue in this discussion, 

 suspended at least until a much larger, and perhaps an en- 

 tirely rewritten accumulation of data on all of the above 

 questions has been made, I feel justified, at this time, in 

 drawing the following tentative conclusions : 



Minor: That 



Our present incubation records include the trme and the 

 apparent lengths, the latter in the majority, probably. 



The irue length of incubation can be shortened (arti- 

 ficially) with extreme difficulty, but prolonged with ease. 



The true length of incubation is loosely related to the 

 size of the species, and still more loosely to the size of the 

 egg, 



There is little or no relation between the true length of 

 incubation and precocity. 



There is no relation between the true length of incuba- 

 tion and the longevity of the species, nor between it and the 

 body-weight : egg- weight index. 



There is no relation between the true length of incuba- 

 tion and the age of the female, or the size of the egg yolk, 



Condition of the parents, faithfulness of the parents 

 while incubating, viability of the egg, thickness of the egg 

 shell, and influences listed under the head of "Telluric Con- 

 ditions," have no lasting effect on the true length of incu- 

 bation; when any of these conditions seem to modify the 

 incubation length, it is merely an action of slowing the 

 embryonic development, and causes no permanent change in 

 the length of the incubation period. 



Major : That 



There is a true or specific length of incubation, 



The true or specific length of incubation is a deep-seated, 



inelastic, and persistently unchanging (in human time 



measures) character. 



Bird temperatures are closely related to the taxonomic 

 "lowness" or "highness" of the species ; 



A bird's temperature determ,ines, or fixes, the true length 

 of its incubation period, and that only an abiding change in 



76 



