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. Neither do these attain to any size in any other species
than that with which we are all familiar. A similar distinction may be
made generally in the case of all Testacea. For there is a great
difference in the edible qualities of the flesh of different kinds;
and in some, moreover, the residual substance known as the mecon is
good for food, while in others it is uneatable. This mecon in the
turbinated genera is lodged in the spiral part of the shell, while
in univalves, such as limpets, it occupies the fundus, and in bivalves
is placed near the hinge, the so-called ovum lying on the right; while
on the opposite side is the vent. The former is incorrectly termed
ovum, for it merely corresponds to what in well-fed sanguineous
animals is fat; and thus it is that it makes its appearance in
Testacea at those seasons of the year when they are in good condition,
namely, spring and autumn. For no Testacea can abide extremes of
temperature, and they are therefore in evil plight in seasons of great
cold or heat. This is clearly shown by what occurs in the case of
the sea-urchins. For though the ova are to be found in these animals
even directly they are born, yet they acquire a greater size than
usual at the time of full moon; not, as some think, because
sea-urchins eat more at that season, but because the nights are then
warmer, owing to the moonlight. For these creatures are bloodless, and
so are unable to stand cold and require warmth
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