164 
EGGS OF BIRDS. 
the egg dropped into the nest of a bird on the point of sitting’, it would 
most certainly be hatched as long before the eggs of the bird whose 
nest it was deposited in as it had been forwarded in the uterus. It has 
frequently been observed, that where the egg of a cuckoo has been 
found in the nest of a bird together with some of its own, that the 
cuckoo’s egg is hatched first. ‘ This seems difficult to account for, 
unless upon the principle we have suggested, as the egg of that bird is 
rather superior in size to that of any bird whose nest it makes choice 
of to deposit it in; amongst which the yellowhammer’s is the largest, 
weighing in general from thirty-six to forty-six grains ; whereas that 
of the cuckoo weighs from forty-four to fifty-four grains. The other 
birds which the cuckoo more generally chooses to incubate its egg, 
seldom produce eggs above forty grains in weight,' and mostly from 
thirty to thirty-six ; if, therefore, the embryo of the cuckoo was not 
sometimes enlarged before the egg was laid, is it reasonable to suppose 
it would be first hatched ? 
In respect to the young cuckoo suffering the hedge-sparrow’s eggs to 
remain in the nest, as above-mentioned, which is contrary to the general 
rule, we can only suppose some defect existed in the young cuckoo, or 
that these eggs were so placed in some small cavity in the bottom of 
the nest that its utmost efforts could not disengage them. These and 
other accidental causes are much more likely, than that the hedge- 
sparrow should lay these adcUtional eggs at the time she was performing 
the act of nutrition to her supposed offspring. 
From late observation we conclude the female cuckoo retires from 
the male so soon as she feels an inclination to deposit an egg, and does 
not admit him again while she is capable of laying, — all the eggs of the 
first set being fecundated at the same time. This, indeed, is probable 
with respect to all birds, though it is difficult to ascertain how the 
prolific quality is regulated so as only to affect such a portion of eggs 
in the ovarium; ^ and that every particular species should almost in- 
variably lay the same quantity. 
The extraordinary growth of a young cuckoo is no more than what 
happens with others produced from eggs of a disproportionate size ; for 
instance, the egg of a raven is not half the size of that of the kite, and 
yet the young of the former are not longer arriving at maturity than 
the latter. Some birds are hatched blind, and entirely naked ; others 
* Jenner, Nat. Hist, of the Cuckoo, p. 3. 
^ Domestic fowls, separated from the male after the first impregnation, are known to 
lay many prolific eggs. — Young on Turkeys, in Nat. Hist, of Norfolk. 
