4 
232 Mr . Jenner’s Obfervaiions on the 
fofter-parents feed it more than five weeks after this period ; 
fo that, if a Cuckoo fhould be ready with an egg much fooner 
than the time pointed out, not a fugle nettling, even one of 
the earlieft, would be fit to provide for itfelf before its parent 
would be inftindtively directed to feek a new refidence, and be 
thus compelled to abandon its young one; for old Cuckoos 
take their final leave of this country the firfl week in July. 
Had nature allowed the Cuckoo to have ftaid here as long 
as fome other migrating birds, which produce a fugle let of 
young ones (as the Swift or Nightingale, for example), and had 
allowed her to have reared as large a number as any bird is 
capable of bringing up at one time, thefe might not have been 
fufficient to have anfwered her purpofe; but by fending the 
Cuckoo from one neft to another, (he is reduced to the lame 
If ate as the bird whofe neft we daily rob of an egg, in which 
cafe the ftimulus for incubation is fufpended. Of tins we have 
a familiar example in the common domeftic fowl. That the 
Cuckoo actually lays a great number of eggs, difl'eftion feems 
to prove very decifively. Upon a companion I had an oppor- 
tunity of making between the ovarium, or racemus vitellorum,- 
•of a female Cuckoo, killed juft as fhe had begun to lay, and of 
a pullet killed in the fame ftate, no eftential difference ap- 
peared. Tiie uterus of each contained an egg perfectly formed, 
and ready for exclusion ; and the ovarium exhibited a large 
clufter of eggs gradually advanced from a very diminutive lize, 
to the greateft the yolk acquires before it is received into the 
oviduct. The appearance of one killed on the third of July 
was very different. In this I could diftindtly trace a great 
number of the membranes which had difeharged yolks into 
the oviduft ; and one of them appeared as if it had parted 
with a yolk the preceding day. The ovarium ft ill exhibited a 
cl u tier 
