148 
THE NATURAL HISTORY 
[LETT. 
as tlie 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 A'ain, martins will breed on for several 
years togetlier 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 ail ; but 
is rendered soft and warm, and fit for incubation, by a lining of 
small straws, grasses, and feathers ; and sometimes 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 assiduity, 
carry out what comes away from their young. Were 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 ; particularly among dogs and cats, 
Avhere 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 enveloped in a tough kind of jelly, and 
therefore is the easier conveyed off without soiling or daubing. 
Yet, as N'ature is cleanly in all her ways, the young perform 
this office for themselves in a little time by thrusting their tails 
out at the aperture of their nest. As the young of small birds 
presently arrive at their 7]\iKia, or full growth, they soon becom_e 
impatient of confinement, and sit all day with their heads out 
of the orifice, where the dams, by clinging to the nest, supply 
them with food from morning to night. Tor a time the young 
are fed on the wing by their parents ; but the feat is done by 
so quick and almost imperceptible a slight, that a person must 
have attended very exactly to their motions before he would be 
able to perceive it. As soon as the young are able to shift for 
themselves, the dams immediately turn their thoughts to the 
business of a second brood, while the first flight, shaken off 
