OBSERVATIONS ON THE CUCKOO. 53 
when it usually ceases; indeed the disposition for 
throwing out the egg appears to cease a few days 
sooner, for the young Cuckoo, after it has been 
hatched nine or ten days, will frequently remove a 
nestling which has been placed in the nest with it, 
when it will suffer an egg, put there at the same time, 
to remain unmolested. The singularity of its shape 
is well adapted to these purposes; for, different from 
other newly hatched birds, its back, from the scapule 
downwards, is very broad, with a considerable de- 
pression in the middle, which seems formed by nature 
for the design of giving a more secure lodgment to 
any object that the young Cuckoo may be desirous of 
removing from the nest. When it is about twelve 
days old, this cavity is quite filled up, and then the 
back assumes the shape common to nestling birds in 
general. The same instinctive impulse which directs 
the Cuckoo to deposit her eggs in the nests of other 
birds, directs her offspring to throw out the eggs 
and young of the owners of the nests. ‘The scheme 
of nature would be incomplete without it; for it 
would be extremely difficult, if not impossible, for 
the small birds, destined to find support for a young 
Cuckoo, to find it for their own young ones also, after 
a certain period; nor would there be room for the 
whole to inhabit the nest. 
The eggs of the Cuckoo are remarkably small in 
proportion to the size of the bird; they also vary 
considerably in size, weight, and colour. It some- 
