A snake has also been observed with two heads for the same reason,
this class also being oviparous and producing many young.
Monstrosities, however, are rarer among them owing to the shape of the
uterus, for by reason of its length the numerous eggs are set in a
line.
Nothing of the kind occurs with bees and wasps, because their
brood is in separate cells. But in the fowl the opposite is the
case, whereby it is plain that we must hold the cause of such
phenomena to lie in the material. So, too, monstrosities are
commoner in other animals if they produce many young. Hence they are
less common in man, for he produces for the most part only one young
one and that perfect; even in man monstrosities occur more often in
regions where the women give birth to more than one at a time, as in
Egypt. And they are commoner in sheep and goats, since they produce
more young. Still more does this apply to the fissipeds, for such
animals produce many young and imperfect, as the dog, the young of
these creatures being generally blind. Why this happens and why they
produce many young must be stated later, but in them Nature has made
an advance towards the production of monstrosities in that what they
generate, being imperfect, is so far unlike the parent; now
monstrosities also belong to the class of things unlike the parent.
Therefore this accident also often invades animals of such a nature.
So, too, it is in these that the so-called 'metachoera' are most
frequent, and the condition of these also is in a way monstrous, since
both deficiency and excess are monstrous.
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