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On The Generation Of Animals   

both the wings and the semen are made from residual matter, nature
cannot afford to spend much upon both. And for this same reason the
birds of prey are neither given to treading much nor to laying many
eggs, as are the heavy birds and those flying birds whose bodies are
bulky, as the pigeon and so forth. For such residual matter is
secreted largely in the heavy birds not given to flying, such as
fowls, partridges, and so on, wherefore their males tread often and
their females produce much material. Of such birds some lay many
eggs at a time and some lay often; for instance, the fowl, the
partridge, and the Libyan ostrich lay many eggs, while the pigeon
family do not lay many but lay often. For these are between the
birds of prey and the heavy ones; they are flyers like the former, but
have bulky bodies like the latter; hence, because they are flyers
and the residue is diverted that. way, they lay few eggs, but they lay
often because of their having bulky bodies and their stomachs being
hot and very active in concoction, and because moreover they can
easily procure their food, whereas the birds of prey do so with

Small birds also tread often and are very fertile, as are
sometimes small plants, for what causes bodily growth in others turn
in them to a seminal residuum. Hence the Adrianic fowls lay most eggs,
for because of the smallness of their bodies the nutriment is used
up in producing young. And other birds are more fertile than
game-fowl, for their bodies are more fluid and bulkier, whereas
those of game-fowl are leaner and drier, since a passionate spirit
is found rather in such bodies as the latter. Moreover the thinness
and weakness of the legs contribute to making the former class of
birds naturally inclined to tread and to be fertile, as we find also
in the human species; for the nourishment which otherwise goes to
the legs is turned in such into a seminal secretion, what Nature takes
from the one place being added at the other. Birds of prey, on the
contrary, have a strong walk and their legs are thick owing to their
habits, so that for all these reasons they neither tread nor lay much.
The kestrel is the most fertile; for this is nearly the only bird of
prey which drinks, and its moisture, both innate and acquired, along
with its heat is favourable to generative products. Even this bird
does not lay very many eggs, but four at the outside.

The cuckoo, though not a bird of prey, lays few eggs, because it
is of a cold nature, as is shown by the cowardice of the bird, whereas
a generative animal should be hot and moist. That it is cowardly is
plain, for it is pursued by all the birds and lays eggs in the nests
of others.

The pigeon family are in the habit of laying two for the most
part, for they neither lay one (no bird does except the cuckoo, and
even that sometimes lays two) nor yet many, but they frequently
produce two, or three at the most generally two, for this number
lies between one and many.

It is plain from the facts that with the birds that lay many eggs
the nutriment is diverted to the semen. For most trees, if they bear
too much fruit, wither away after the crop when nutriment is not
reserved for themselves, and this seems to be what happens to annuals,
as leguminous plants, corn, and the like. For they consume all their
nutriment to make seed, their kind being prolific. And some fowls
after laying too much, so as even to lay two eggs in a day, have
died after this. For both the birds the plants become exhausted, and
this condition is an excess of secretion of residual matter. A similar
condition is the cause of the later sterility of the lioness, for at
the first birth she produces five or six, then in the next year
four, and again three cubs, then the next number down to one, then
none at all, showing that the residue is being used up and the

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