ion. In China
the production of eggs is confined to certain favourable districts, and the
raisers are precluded by law from producing silk, so that their whole
attention may be necessarily given up to this one object.[502]

The following details on the differences between the several breeds are
taken, when not stated to the contrary, from M. Robinet's excellent
work,[503] which bears every sign of care and large experience. The
_eggs_ in the different races vary in colour, in shape (being round,
elliptic, or oval), and in size. The eggs laid in June in the south of
France, and in July in the central provinces, do not hatch until the
following spring; and it is in vain, says M. Robinet, to expose them to
a temperature gradually raised, in order that the caterpillar may be
quickly developed. Yet occasionally, without any known cause, batches
of eggs are produced, which immediately begin to undergo the proper
changes, and are hatched in from twenty to thirty days. From these and
some other analogous facts it may be concluded that the Trevoltini
silkworms of Italy, of which the caterpillars are hatched in from
fifteen to twenty days, do not necessarily form, as has been
maintained, a distinct species. Although the breeds which live in
temperate countries produce eggs which cannot be immediately hatched by
artificial heat, yet when they are removed to and reared in a hot
country they gradually acquire the character of quick development, as
in the Trevoltini races.[504]

_Caterpillars._--These vary greatly in size and colour. The skin is
generally white, sometimes mottled with black or grey, and occasionally
quite black. The colour, however, as M. Robinet asserts, is not
constant, even in perfectly pure breeds; except in the _race tigree_,
so called from being marked with transverse black stripes. As the
general colour of the caterpillar is not correlated with that of the
silk,[505] this character is disregarded {302} by cultivators, and has
not been fixed by selection. Captain Hutton, in the paper before
referred to, has argued with much force that the dark tiger-like marks,
which so frequently appear during the later moults in the caterpillars
of various breeds, are due to reversion; for the caterpillars of
several allied wild species of Bombyx are marked and coloured in this
manner. He separated s