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means of escaping that risk, and, as a consequence, one 
definite transmutation of a group. We have, then, to ask 
whether the insect world is liable to only one great risk, 
the risk of being seen and therefore captured by their 
enemies ; only one mode of defence, the adoption of 
certain colours, whether the object be to conceal, to warn, 
or to mimic. 
It may be questioned whether we could find in any 
sphere of nature a single illustration of the principle, “one 
risk,one remedy”; certainly it is not so in the insect world, 
with which we are at present more especially concerned. 
We know that insects are liable to various dangers besides 
those which arise from being visible to the enemies which 
prey upon them in their perfectly developed forms. In 
the earliest stage, they are liable, as we have just heard, to 
suffer from the attacks of parasites, which lay eggs in their 
eggs. The larvae which are hatched from eggs which have 
been thus treated simply afford temporary board and 
lodging for the parasite, and perish miserably. In the 
case just cited only twenty survive out of two hundred. 
Nine-tenths of the individuals had succumbed before they 
were subjected to the selective process which the theory 
supposes to account for defensive colouring. 
But, apart, from parasites, insects have other difficulties 
to encounter before they reach their last stage of develop 
ment. It is true that the birds which prey upon the imago 
disappear with the approach of winter. 
“Many of our migrant singers, like the swallows, eat only such 
things as they can catch in their swift flight, open-mouthed, through 
the air ; these are few and far between in the raw and cold atmos 
phere of winter here. Swift and swallow, nightingale and cuckoo, 
warbler, wheatear, whinchat, blackcap, wryneck, flycatcher,—all the 
merry troupe of strolling singers must follow the sun and the 
creatures that dance in the sunbeams to lands that are sunny in 
winter.”—( 1 he Cornhill Magazine. New series. vol. xx //., 
pp. 164-165.)