506 REPTILES AND BIRDS. 
three feet in depth, at the extremity of which they place their nest. 
Sometimes the nursery of their young is formed of twigs torn by the 
bird from the dead branches of trees, and bound together by a viscous 
liquid which flows from its mouth. 
When, after a month’s labour, the Swallows have finished their 
dwellings, the female deposits from four to six eggs. Incubation 
commences, and continues from twelve to fifteen days, during which 
the male bird exhibits intense interest in the proceedings, carrying 
food continually to his mate, and passing the night in her immediate 
vicinity, twittering and chirping all day long to cheer the mother at 
her task. ‘Two or three times in the season they thus raise a family. 
From the time when the little ones are hatched the parent birds 
attend them with all the care their feebleness demands, and often ex- 
hibit remarkable proofs of affection. When the young Swallows feel 
strong enough to try their wings, the old ones tenderly guide them on 
their first attempts at flight, and teach them how pursuit of insects in 
the air is successfully performed. Boerhaave quotes an instance 
where a Swallow, returning from some distant excursion, found the 
house in which it had built its nest in flames. It did not hesitate an 
instant to dash into the fire to try and save its young. 
Swallows generally prefer the proximity of a lake or river, the 
surface of water being always the rendezvous of crowds of in- 
sects, among which they reap a plentiful harvest. Extremely so- 
ciable, they assemble in large flocks, and appear to be bound together 
by strong attachment, for they aid each other in trying circum- 
stances. 
**T have seen an unfortunate swallow,” says Dupont de Nemours, 
“which had, I know not how, entangled its foot in a long thread, 
one end of which was attached to the roof of the College of the 
Four Nations; its strength was exhausted, and it hung uttering 
painful cries at the end of the line, endeavouring to release itself 
occasionally by futile attempts at flight. All the swallows between 
the Tuileries and the Pont Neuf, and perhaps for a much greater 
distance, were assembled around the unfortunate bird, to the number 
of many thousands, forming a perfect cloud. All that came flew past, 
giving a peck of their bills to the fatal thread; these blows, being 
frequently repeated, and always directed at the same spot, were finally 
successful, for in half an hour the line was cut and the captive set 
at liberty.” 
Another fact, related by the great naturalist Linnzeus, proves how 
strong is the spirit of brotherhood with these birds. When some swal- 
lows returned in spring to take possession of their nests, a certain 
