54 NATURAL HISTORY OF SELBORNE 



But then, that this work may not, while it is soft and green, 

 pull itself down by its own weight, the provident architect 

 has prudence and forbearance enough not to advance her 

 work too fast ; but by building only in the morning, and by 

 dedicating the 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 become top- 

 heavy, and so be ruined by its own weight. By this method 

 in about ten or twelve days is formed an hemispheric 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 incuba- 

 tion, 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. 

 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; particularly among dogs and cats, where the dams 



