occupied by Birds in Incubation. 91 



a Raveu's, instead of taking about four days longer ; and that 

 a Long-eared OwFs would take almost exactly the same time 

 as a Ring Dove's, instead of half as long again. 



Tiedemann, after remarking that " the duration of incu- 

 bation differs rauch/^ makes the following statement : — " In 

 general one finds that it is in proportion to the degree of 

 development which the embryo reaches in the egg, so that 

 birds whose embryo leaves the egg little developed and formed, 

 incubate a shorter time than those whose embryo is hatched 

 much developed. To those whose embryo leaves the egg 

 little developed belong the Birds of Prey, the Passeres (Sing- 

 vogel), and the Picaria (Klettervogel).''^ The inclusion of 

 the Birds of Prey in the group is unfortunate for the theory, 

 for instead of having a short period of incubation, as Tiede- 

 mann supposed, they undoubtedly have a long one. The 

 rule, no doubt, applies in many cases, but clearly not in all, 

 for the Diurnal Birds of Prey, the Owls, and the Gannets, 

 for example, all incubate for more or less protracted periods, 

 yet their young are particularly helpless when hatched. 



In conclusion, I must acknowledge the great obligations I 

 am under to many friends (too numerous to particularize 

 here) for invaluable assistance rendered in a variety of ways. 

 To one and all I now return my sincerest thanks. 



List of Works referred to. 



Audubon's ' Ornithological Biography.' (5 vols.) 1831. 



Badminton Library — ' Shooting.'' (2 vols.) 1886. 



Bechstein's 'Natural History of Cage Birds.' 3rd ed. 

 1812. (Translated 1837). 



Booth's ' Rough Notes.' (Part 5.) 1883. 



Brehm's ' Thierleben.' (2nd ed., 3 vols.) 1878. 



Cassell's ' Book of Birds,' from the text of Brehm, by 

 T. Rymer Jones. (4 vols.) (N. D.) 



Dresser's 'Birds of Europe.' (8 vols.) 1871-1881. 



'Field' Newspaper. Various years, 1871 &c. 



Glasgow Nat. Hist. Society, Proceedings of. (Vol. II.) 

 1873-76. 



Gould's ' Birds of Europe.' 1837. 



