Natural Sciences of Philadelphia 
43 
It seems desirable to make this fact clear both to our members 
and visitors and to explain the extent, relationship and objects of 
the several collections in each department, so that a clearer con¬ 
ception of our needs and resources may be obtained, and in this 
year’s report we propose to consider the department of birds, as 
being perhaps best calculated to illustrate the subject. 
When a corps of specialists in the various branches of natural 
history took the place of the single museum curator of old, their 
duties were not only the supervision of the exhibits in their re¬ 
spective departments, but also the prosecution of original research. 
This necessitated the acquisition of many more specimens than the 
two or three-of each kind which formed the mounted collection in 
the exhibition hall. There must be specimens showing variation 
due to sex, age, season and environment. Furthermore, the speci¬ 
mens must be of a character suitable for easy handling, and com¬ 
parison. Thus was developed the skin collection, a bird '‘skin” 
being a stuffed specimen, resembling a dead bird lying on its back 
with its wings close to the body, but without the glass eyes, wires, 
etc., characteristic of the mounted specimen. The wings, feet, 
bill and feathers of such a specimen may be examined with ease 
which is not possible with a mounted bird, and if the need arises 
a skin may be relaxed by steaming and can be mounted if desired. 
The museum’s “study collection” of skins is very much larger 
than the exhibition collection of mounted birds, for several reasons. 
As already stated a series of specimens is required for the research 
work being carried on in the department, far larger than the number 
needed for exhibition; then again many closely allied forms which 
would not be distinguished by the average visitor are preserved 
only in the study collection and so also with most of the very rare 
or historic specimens. The reason for this is a very important one, 
namely that the colors of bird plumage are seriously affected by light, 
and a mounted specimen even though not exposed to direct sunlight 
will inevitably fade and is soon useless for scientific study. The 
extend of fading varies in different species, and many specimens 
that have become useless for technical research, retain their colors 
sufficiently well to serve as exhibits for many years. 
It should be clear to anyone, however, that the only reliable, 
permanent collection of birds is the study collection of skins. It 
can be constantly added to and brought nearer and nearer to com- 
