TFeif/ht of Birds' Eggs during Incuhation. 137 



C. dauricus and the dark <\ negledus, many intermediate 

 forms occur, we must be led to believe that these inter- 

 mediate forms are hybrids and that C. dauricus and 

 C. neglectus are distinct species. All recent (Styaii and 

 La Touche) and earlier observers (Swinhoe and David) 

 had not the least doubt as to the specific value of the two 

 forms, and I quite agree with them. Of the same opinion 

 seems to be my friend Mr. Dresser, who I think was 

 not much at fiiult (Man. Pal. B. p. 420) in considering 

 C. negledus a distinct subspecies of ('. monedula, to which 

 Swinhoe, Giglioli, and others positively say that C. neglectus 

 is nearly allied. All field-naturalists who have observed 

 the two forms state that they are frequently found together, 

 and we may suppose it possible that the birds not infrequently 

 have the habit of losing sight of their proper mates. 



V. — On the Decrease in fVeight of Birds' Eggs during 

 Incubation. By Elizabeth Seymour Norton, F.Z.S."^ 



(Text-fig. 6.) 



Circumstances arose last summer which made me curious 

 to ascertain whether a partially-incubated Thrush's egg could 

 be distinguished from a new-laid egg by its weight. The 

 natural inference, in the absence of definite knowledge, 

 seemed to be that an egg containing a living, breathing chick 

 would be heavier than an egg containing only the nearly 

 fluid " yolk and white.'' A few books that I consulted told 

 me nothing with regard to the weight of eggs ; so I began 

 a series of incubations of hens' eggs to find out for myself 

 what occurred. I soon discovered that all the eggs decreased 

 in weight as incubation advanced. 



After reaching this conclusion I came across the " Note " 

 by Mr. Hugh S. Gladstone which was published iu ' The Ibis ' 

 of 1904 (p. 376) . Mr. Gladstone shewed the average decrease 

 of Pheasants' eggs during incubation to be a little over 14 



* Communicated by Mr. W. P. Pycraft, F.Z.S., M.B.O.U. 



