137 
Weight of Birds’ Eggs during Incubation. 
C. dauricus and the dark C. neglectus, 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 (Styan and 
La Touche) and earlier observers (Swinlioe 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 fault (Man. Pal. B. p. 420) in considering 
C. neglectus a distinct subspecies of C. monedula , to which 
Swinhoe, Gigliolh, and others positively say that 0. 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 Weight of Birds’ Eggs during 
Incubation. By Elizabeth Seymour Norton, E.Z.S.* 
(Text-fig. 6.) 
Circumstances arose last summer which made me curious 
to ascertain whether a partially-incubated Thrushes egg could 
be distinguished from a new-laid egg by its w T eight. 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 in f The Ibis 5 
of 1904 (p. 376). Mr. Gladstone shewed the average decrease 
of Pheasants’ eggs during incubation to be a little over 14 
* Communicated by Mr. "VV. P. Pycraft, F.Z.S., M.B.O.U. 
