EGGS OF BIRDS. 
165 
possess the organs of sight, and are covered with down. Those birds 
who feed and breed on the ground, and never perch on trees, are gene- 
rally provided with warm covering, and have the use of their eyes and 
legs soon after they are excluded from the egg.^ These are not fed by 
the parent bird, being more perfectly formed when hatched, but soon 
discover by instinct their proper food ; on the contrary, predacious 
birds are totally helpless at first, though warmly clothed with down. 
The extraordinary and rapid growth of the egg is also worthy notice. 
We before observed there is a line drawn by nature, to prevent more 
than a certain quantity of eggs, peculiar to each species, being fecun- 
dated at once ; otherwise a bird in one season might produce all the 
eggs she possessed, and afterguards become useless in propagation. 
But notwithstanding only a portion of the ovaries are impregnated 
at the same time, yet the stimulus to love considerably increases the 
size of all the eggs in the ovarium. When this stimulus ceases, be it 
from what cause it may, the organic particles cease to flow to that part ; 
therefore, as a redundance of organic particles excite love by distending 
those parts necessary for production, so, on the contrary, the want of a 
sufficient quantity reduces them to their primitive state. It seems ab- 
solutely necessary that a dilatation of the ovaries should take place 
before they can be fecundated ; and that, by the law of nature, only a 
certain number should be sufficiently large to be impregnated at the 
same time ; and that no others can possibly receive the male stimulus 
till after the first set are produced. We have before remarked, a super- 
abundance of organic particles is cause sufficient to separate an egg 
from the ovarium without male contact. It is possible a bird, in its 
natural state, may lay an egg unimpregnated, which may account for 
addled eggs being found in nests. We once found a whitethroat sitting 
on four eggs perfectly dried up. This also seems to prove that birds do 
not know the necessary time of incubation. 
The growth of an egg after impregnation is exceedingly rapid ; the 
yolk only is formed in the ovarium., where it remains till within twenty- 
four hours of its being produced ; when that part is fully matured, it 
separates and falls down the oviduct into the uterus, where the egg is 
perfectly formed ; first, the vitellus or yolk is surrounded by the albu- 
men or white ; and lastly is covered with a calcareous shell.^ The very 
expeditious growth of these last appear to be an extraordinary exertion 
* With a few exceptions. Some that occasionally perch have these properties. 
“We do not mean to enter minutely into the physiological description of an egg, 
which may be found in various publications. 
