Notes in 1887 upon lepidopterous larva, éc. 579 
sradually overtakes and passes that of S. ligustri. The 
newly-hatched S. ligustri is much larger than the other 
species, and its rate of growth during the Ist stage is 
much greater: in the 2nd stage the growth is almost 
exactly equal: in the 3rd stage S. convolvuli rapidly 
overtakes S. ligustri, so that the larve are of nearly equal 
lengths at the end of this stage: soon after the beginning 
of the 4th stage S. convolvuli passes the other larva, and 
in the last stage the differences are increased to a much 
ereater extent, in the normal condition, although the 
diagram indicates an equal rate of growth. 
Such facts seem to indicate a comparatively recent 
increase in the size of S. convolvuli, an increase which is 
only manifest in the later stages, and has not yet passed 
back to the younger larve or the egg. In two such closely- 
allied species the relative sizes at the beginning of ontogeny 
probably indicate (unless they are explicable as adapta- 
tions) the former relative sizes at the end of larval onto- 
geny, and the relative sizes of pupz and imagines. And 
there may be good reasons for a recent alteration in the 
size of S. convolvult. I have shown that size in itself may 
be a protection against the smaller enemies of a species 
(Proc. Zool. Soc., March, 1887, pp. 240, 241). A larva 
which feeds upon a creeping food-plant comes especially 
within the reach of insect-eating reptiles and mammals, 
and it would certainly stand a better chance of escaping 
these by an increase from a medium to a large size; and 
this is also true of the imago, which lays eggs on the 
plant, and emerges from the pupa near to the plant. 
It is probable that a similar explanation holds in the 
case of Acherontia atropos, and it would be most in- 
teresting to obtain measurements of this latter larva in 
all stages. The fact that other small Sphingide feed 
upon low-growing plants is no objection to this argument. 
Difficulties are met by different species in various ways. 
There will be a frequent tendency towards reduction in 
size in order to assist in concealment; but a large larva, 
which, by a change of food-plant, or a change in the 
habit of its food-plant, was brought within reach of a 
large number of the smaller insect-eating vertebrates, 
would sometimes tend to seek protection in the opposite 
manner; and the diagram strongly supports the suppo- 
sition that such changes have actually taken place in 
S. convolvult. 
