EGGS OF BIRDS. 
163 
of the breed. It is but few birds, if any, that would produce a second 
lot of eggs in the same season if unmolested ; but if their nests are 
destroyed, it is probable three or four separate lots may be protruded. 
We have never been able to discover with certainty, either in the 
red-breast or hedge-sparrow, who are the earliest breeders, the produc- 
tion of a second brood after the first has been brought to maturity. 
Their attention to their young continues long after they leave the 
nest. The great exertion to collect food for so many must exhaust 
the animal spirits, to recruit which is a work of time ; so that the 
season is too far advanced for a second production. The secondary eggs 
being brought forward is not elfected by the will of the bird, but is 
caused by the dictates of nature, the impulse of love. 
We shall here take notice of the eggs of a hedge-sparrow being found 
in a nest of that bird in a prolific state, and a young cuckoo of a fortnight 
old covering them, as related by Dr. Jenner, in order to strengthen a 
supposition we shall hereafter mention. May not this be owing to a 
very different cause than what has been suspected ? If the cuckoo had 
dropped an egg into the hedge-sparrow’s nest before it was finished, it 
is unlikely it would have been suffered to remain ; but even suppose it 
had, it would not have been sat on till the hedge-sparrow began to in- 
cubate her own eggs ; consequently the cuckoo’s egg, which is largest, 
could not be hatched before the others in the common course of nature. 
Again : if we suppose the hedge-sparrow had previously laid her eggs, 
which she sat on together with the cuckoo’s, and that the young 
cuckoo, soon after it was hatched, had turned out of the nest the eggs 
or young of the hedge-sparrow, which is the natural consequence, how 
should these eggs come into the nest containing a living fcetus ? It is 
very improbable a bird should lay eggs in a nest where she had young, 
for such we may call the young cuckoo, the hedge-sparrow not know- 
ing the difference. If birds were capable of this, it would be similar to 
superfetation in viviparous animals, of which there are but few instances. 
We can therefore only account for this singular circumstance by supposing 
the cuckoo is actually endowed wiljh the property of retaining its egg- 
in the uterus, after it is matured, till it has discovered a nest in a state fit 
to deposit it. The consequence of this retention would be a dilatation 
of the embryo by the internal heat of the body, > and the. foetus advanced 
towards perfection in proportion to the time the egg remained in that 
state. Of course, after such a previous enlargement of the foetus, were 
‘ The viper is oviparous, or rather ove-viparous, hatching its young by the internal 
heat of its body. 
M 2 
