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. Therefore it is that
they are found in better condition in summer than at any other season;
and this all over the world excepting in the Pyrrhean tidal strait.
There the sea-urchins flourish as well in winter as in summer. But the
reason for this is that they have a greater abundance of food in the
winter, because the fish desert the strait at that season.
The number of the ova is the same in all sea-urchins, and is an
odd one. For there are five ova, just as there are also five teeth and
five stomachs; and the explanation of this is to be found in the
fact that the so-called ova are not really ova, but merely, as was
said before, the result of the animal's well-fed condition. Oysters
also have a so-called ovum, corresponding in character to that of
the sea-urchins, but existing only on one side of their body. Now
inasmuch as the sea-urchin is of a spherical form, and not merely a
single disk like the oyster, and in virtue of its spherical shape is
the same from whatever side it be examined, its ovum must
necessarily be of a corresponding symmetry.
Pages:
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188