182 
NATURAL HISTORY 
vident arcMtect has prudence and forbearance enougli not 
to advance her work too fast ; but by building only in tlie 
morning, and by dedicating tbe rest of the day to food and 
amusement, gives it sufficient time to dry and harden. 
About half an inch seems to be a sufficient layer for a day. 
Thus careful workmen when they build mud walls (informed 
at first perhaps by this little bird) raise but a moderate 
layer at a time, and then desist; lest the work should be- 
come top-heavy, and so be ruined by its own weight. By 
this method in about ten or twelve days is formed an hemi- 
spheric nest with a small aperture towards the top, strong, 
compact, and warm ; and perfectly fitted for all the purposes 
for which it was intended. But then nothing is more 
common than for the house sparrow, as soon as the shell is 
finished, to seize on it as its own, to eject the owner, and to 
line it after its own manner. 
After so much labour is bestowed in erecting a mansion, 
as Nature seldom works in vain, martins will breed on for 
several years together in the same nest, where it happens to 
be well sheltered and secure from the injuries of weather. 
The shell or crust of the nest is a sort of rustic-work full of 
knobs and protuberances on the outside : nor is the inside 
of those that I have examined smoothed with any exactness 
at all ; but is rendered soft and warm, and fit for incubation, 
by a lining of small straws, grasses, and feathers ; and some- 
times by a bed of moss interwoven with wool. In this nest 
they tread, or engender, frequently during the time of 
building ; and the hen lays from three to five white eggs. 
At first when the young are hatched, and are in a naked 
and helpless condition, the parent birds, with tender assi- 
duity, carry out what comes away from their young. Was 
it not for this affectionate cleanliness the nestlings would 
soon be burnt up, and destroyed in so deep and hollow a 
nest, by their own caustic excrement. In the quadruped 
creation, the same neat precaution is made use of ; particu- 
larly among dogs and cats, where the dams lick away what 
proceeds from their young. But in birds there seems to be 
a particular provision, that the dung of nestlings is en- 
veloped in a tough kind of jelly, and therefore is the easier 
