335 
the nests of the Java swallow. 
while the sun is fertilizing them, and therefore has probably 
an equally abundant supply of its natural food in the regions 
of the north, as at the equator. 
The only difference between the glands of the migrating 
swallow, and those of the blackbird, is the smallness of the 
reservoir, the surface of the gullet upon which the external 
openings of the glands are seen is exactly the same, there is 
not in the one or the other any apparatus for secreting 
mucus which is not common to birds in general. 
In the Java swallow we have, on the other hand, a struc- 
ture of a particular nature ; there is a membranous tube sur- 
rounding the duct of each of the gastric glands, which, after 
projecting into the gullet for a little way, splits into separate 
portions like the petals of a flower : for what purpose so ex- 
traordinary an apparatus could be provided, would probably 
have puzzled the weak intellects of human beings, and many 
wild theories might have been formed respecting it, had not 
the animal matter of which the bird's nest is composed, and 
the accurate observation of Sir Stamford Raffles, who had 
no doubt that the materials of the nest were produced from 
the gullet, led to the discovery of its use. 
That the mucus of which the nest is composed, is secreted 
from the surface of these membranous tubes, there is no 
more doubt than that the gastric juice is secreted from the 
glands whose ducts these tubes surround ; and this confirms 
an opinion which I have adopted for many years, that mem- 
branes on which no glandular structure could be seen, were 
capable of secreting mucus; and now that we find those 
membranes, where their surfaces are so much magnified, ex- 
hibit no glandular structure, we may, without the chance of 
Xx 
MDCCCXVII. 
