ome caterpillars with the tiger-like marks, and
in the succeeding spring (pp. 149, 298) nearly all the caterpillars
reared from them were dark-brindled, and the tints became still darker
in the third generation. The moths reared from these caterpillars[506]
also became darker, and resembled in colouring the wild _B. Huttoni_.
On this view of the tiger-like marks being due to reversion, the
persistency with which they are transmitted is intelligible.

Several years ago Mrs. Whitby took great pains in breeding silkworms on
a large scale, and she informed me that some of her caterpillars had
dark eyebrows. This is probably the first step in reversion towards the
tiger-like marks, and I was curious to know whether so trifling a
character would be inherited; at my request she separated in 1848
twenty of these caterpillars, and having kept the moths separate, bred
from them. Of the many caterpillars thus reared, "every one without
exception had eyebrows, some darker and more decidedly marked than the
others, but _all_ had eyebrows more or less plainly visible." Black
caterpillars occasionally appear amongst those of the common kind, but
in so variable a manner, that according to M. Robinet the same race
will one year exclusively produce white caterpillars, and the next year
many black ones; nevertheless, I have been informed by M. A. Bossi of
Geneva, that, if these black caterpillars are separately bred from,
they reproduce the same colour; but the cocoons and moths reared from
them do not present any difference.

The caterpillar in Europe ordinarily moults four times before passing
into the cocoon stage; but there are races "a trois mues," and the
Trevoltini race likewise moults only thrice. It might have been thought
that so important a physiological difference would not have arisen
under domestication; but M. Robinet[507] states that, on the one hand,
ordinary caterpillars occasionally spin their cocoons after only three
moults, and, on the other hand, "presque toutes les races a trois mues,
que nous avons experimentees, ont fait quatre mues a la seconde ou a la
troisieme annee, ce qui semble prouver qu'il a suffi de les placer dans
des conditions favorables pour leur rendre une faculte qu'elles avaient
perdue sous des influences moins favorables."

_Cocoons._--The caterpillar in changing