On the low, moist, alluvial soils of the East, slips of this tree are
planted in close and continuous lines, and six to eight weeks afterwards
they are six feet high, and the leaf-crop allows of six to ten broods
being produced in the course of six months. In Europe it is not unusual
for more than one brood to be produced, and the female lays her eggs
towards the end of the summer; but they do not hatch until the following
spring, when the leaves appear. In Asia, during the season, the eggs
hatch eight to ten days after laying. The caterpillar feeds
persistently, and rapidly grows; at the end of a month it moults, and
this happens four times in all before it starts to make its cocoon.
[Illustration: =THE DEVELOPMENT OF THE SILKWORM=
The female moth deposits in July three to five hundred eggs, from which
the white caterpillars (a) emerge in the following spring, at the period
when the white mulberry tree blooms, upon the leaves of which they feed.
The caterpillars change their skins four times and are full grown in
about a month. They now spin a cocoon (c), which is generally completed
in three and a half days, and five days later they change into pupæ (b).
The pupal stage lasts from fourteen to nineteen days. The cocoons
furnish the silk, and the pupæ are generally killed on the tenth day by
heat.]