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. For it
would be in opposition to what prevails in the whole tribe of
Testacea; for in all the ovum is discontinuous, and in all excepting
the sea-urchins asymmetrical, being placed only on one side of the
body. Owing then to this necessary discontinuity of the ovum, which
belongs to the sea-urchin as a member of the class, and owing to the
spherical shape of its body, which is its individual peculiarity, this
animal cannot possibly have an even number of ova. For were they an
even number, they would have to be arranged exactly opposite to each
other, in pairs, so as to keep the necessary symmetry; one ovum of
each pair being placed at one end, the other ovum at the other end
of a transverse diameter. This again would violate the universal
provision in Testacea. For both in the oysters and in the scallops
we find the ovum only on one side of the circumference. The number
then of the ova must be uneven, three for instance, or five. But if
there were only three they would be much too far apart; while, if
there were more than five, they would come to form a continuous
mass. The former arrangement would be disadvantageous to the animal,
the latter an impossibility. There can therefore be neither more nor
less than five. For the same reason the stomach is divided into five
parts, and there is a corresponding number of teeth. For seeing that
the ova represent each of them a kind of body for the animal, their
disposition must conform to that of the stomach, seeing that it is
from this that they derive the material for their growth
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