takes, as, for example, when it is recorded by one writer that 

 the Hummingbird's incubation period is "eighty days." 



There is a singular disagreement in the recorded lengths 

 of incubation of species which might be called semi-domesti- 

 cated, as the white stork, a lack of agreement inexplicable 

 to the writer, unless it be due to faulty observation. 



It is necessary, when analyzing these data, to remember 

 that an agreement in the records quoted by two or more 

 different authorities does not thereby mean that the records 

 are conclusively correct because of such agreement, for one 

 writer may have (and evidently has) copied from another 

 without indicating or crediting such fact. 



Conflicts and lack of consonance in the records of the 

 length of incubation, and inconsistencies of testimony on 

 the same, are not surprising; the writer's slight personal 

 experience in trying to determine accurately the incubation 

 period of a few species has shown him the many difficulties 

 to be encountered and overcome in such a line of work. 

 Many birds abandon a nest (and its eggs) if it be too closely 

 watched, or if the nest be disturbed in the least; and to 

 overcome this difficulty calls for limitless care and patience 

 while observing the nest. It is a time-robbing task to visit 

 a nest daih^, it may be hourly, to ascertain when the eggs 

 are laid, to mark them as laid, and to watch when they 

 hatch, all of which must be done with some species if one 

 is to succeed in making an accurate determination. Newton 

 (25) long ago deplored the scantiness and inaccuracy of the 

 then existing data on incubation, because (he said) correct 

 data were greatly needed to check up and compare the em- 

 bryology of different bird species at relatively the same 

 stages, as an aid to put taxonomy on a sound basis. It is 

 obvious that every ornithologist will concur in this, and the 

 writer hopes to show later on that a more extensive and 

 accurate knowledge of the true length of incubation of dif- 

 ferent species maj^ help the taxonomer otherwise than 

 through embryology. In justice to the multitude of bird 

 students who have contributed indirectly and directly to the 

 present list of incubation periods, one must recall that here- 

 tofore there has been no apparent indication of a need for 

 exactitude in measuring the length of this period. Notwith- 

 standing the unavoidable errors and discrepancies probably 

 embodied in this list, it is a splendid commentary on the 

 enthusiasm, care, patience and self-denial of ornithologists 

 the world over that so many records have been made, many 

 of which are patently of great accuracy. 



From this brief survey of the conflicts in the data, it 

 is evident that this list of incubation periods is made up 

 of both true and apparent lengths of incubation, the latter 

 probably being in the majority, and that it needs more 



14 



