OBSERVATIONS ON THE CUCKOO. 55 
pointed out, not a single nestling, even of the earliest, 
would be fit to provide for itself, before its parent 
would be instinctively directed to seek a new resi- 
dence, and would be thus compelled to abandon its 
young one; for old Cuckoos take their final leave of 
this country in the first week of July. 
If nature had allowed the Cuckoo to stay here as 
long as some other Migratory Birds which produce a 
single set of young ones (as the Swift or Nightingale 
for example), and had allowed it to rear as large a 
number as any bird is capable of bringing up at one 
time, these might not have been sufficient to answer 
her purpose; but by sending the Cuckoo from one 
nest to another, it is reduced to the same state as the 
bird whose nest is daily robbed of an egg, in which 
case the stimulus for incubation is suspended. Of 
this we have a familiar example in the common Do- 
mestic Fowl. That the Cuckoo actually lays a great 
number of eggs, dissection seems to prove very deci- 
sively. Upon comparing the ovarium, or racemus 
vitellorum, of a female Cuckoo, killed just as she had 
begun to lay, with that of a pullet killed just in the 
same state, no essential difference appeared: the 
uterus of each contained an egg perfectly formed 
and ready for exclusion; and the ovarium exhibited a 
large cluster of eggs gradually advanced from a very 
diminutive size to the greatest the yolk acquires be- 
fore it is received into the oviduct. The appearance 
of one killed on the 3rd of July was very different. 
