WATER BIRDS. 209 
the glands, but I have no hesitation in coming to a con- 
clusion which, to my mind, is perfectly satisfactory, and 
that is, that they are simply excretory. In the course 
of my examination of various species, I found that not 
merely were the webs of the feathers of aquatic birds 
oily, but that the shafts and quills were equally so. 
The chief food of most pelagic species is of an oily 
nature; and their stomachs are filled with oil to such an 
extent that, as is well known, the body of a fulmar petrel, 
with a wick of cotton drawn through it, is the common 
lamp of the inhabitants of St. Kilda. I have also often 
seen the Cape pigeon (Daption Capensis) vomit nearly 
a tablespoonful of clear oil when captured. It is evident 
that in these and similar species which seek their food 
on the water, no outward application of oil to their 
feathers is necessary, for both skin, flesh, and feathers 
are thoroughly impregnated with it. 
In support of my view we find, as I said before, that 
those birds whose food is obtained from the water, and 
whose flesh and skin are more or less oily, are fur- 
nished with two glands, in some species of large size ; 
whilst land birds, whose flesh is generally free from oili- 
ness, have only one gland; and in some of these, as in 
the black grouse for instance, it is very small, though 
singularly enough, the red grouse and ptarmigan have 
each two glands, but very small. An apparent excep- 
tion exists in the white-tailed sea eagle, which has, like 
the rest of the rapacious birds, but one gland; but 
though it feeds on fish, which it captures in the water, 
lambs, hares, and other animals also enter largely into 
its diet. But there is another more remarkable exception 
to this arrangement, and one totally incompatible with 
the popular idea, and that is the group of the penguins, 
kg 
