between lepidopterous larve and their surroundings. 317 
hybernation is shown in either fig. 4 or fig. 9 on Plate 
XVII. The latter appearance was a response to an en- 
vironment of lichen-covered sticks; but after October 16th 
these were replaced by black-barked twigs, which it is seen 
produced no effect at all. Again, Plate X VIII, fig. 2 repre- 
sents a later stage of Plate XVII, fig. 6. Here too the 
resemblance between older and younger larve is very close, 
although the former had been subjected to the same black 
environment after October 16th. The negative result 
of a transfer experiment in the opposite direction is seen 
in Plate XVII, fig. 14, the representation of a larva which 
had been exposed to lichen-covered sticks after October 
3rd. All the larvee did not remain as uniform throughout 
their life-history as these three. Thus Plate XVIII, fig. 
3 represents a nearly mature larva of which the appear- 
ance before hybernation is seen in Plate XVII, figs. 4 
or 9. In this case the larva darkened considerably after 
the winter, although its environment had not been shifted, 
but consisted of lichen-covered sticks throughout. 
It is probable that the power of adjustment to environ- 
ment possessed in so marked a degree by this species is 
specially directed to protection during hybernation, when 
the food-plants are leafless, and when enemies are often 
pressed by hunger. But it is doubtless also of importance 
later on when the larva becomes so much larger and would 
on this account be far more conspicuous. It is probable, 
however, that the caterpillar does not wander from its 
food-plant, and that complete adjustment to the old wood 
before hybernation is an adequate defence in the following 
spring and summer. If this be correct there would be no 
advantage in a prolonged larval susceptibility. 
The same relationship between susceptibility and the 
particular needs of each species is seen in the eftect of 
an environment of green leaves and shoots upon G. quer- 
cifolia, O. lidentata, and A. betularia. The first-named 
probably invariably rests by day, except for a brief period 
after leaving the egg, upon the older wood, and the power 
of adjustment to leaves and young shoots, being altogether 
useless to it, has never been acquired. The last-named, 
with its remarkable range of food-plants, including many, 
such as broom or rose, in which green shoots are a 
prominent feature, is frequently in a position in which 
a green colour would best conceal its nearly smooth and 
cylindrical form; and we find that, as a matter of fact, 
