204 SECRETS OF ANIMAL LIFE 
what is for it simply a new and very promiseful 
world, In many cases it is only the mother-animal 
that is parasitic, so that it is not necessarily a selfish 
evasion of struggle this parasitism. It is not easy 
to fence off parasites that may be of a little benefit 
to their hosts from symbions and commensals 
that are, on the whole, beneficial, but levy a slight 
tax. All these linkages are to be looked at broadly 
as expressions of a widespread tendency to weave 
lives together in a web—an external systematiza- 
tion or correlation which has been of great moment 
in evolution. 
Some have explained that it is not the destruc- 
tiveness of parasites that they object to, nor their 
ugliness, nor even their feckless, drifting life, but a 
certain element of devilry. The ichneumon-fly 
lays her eggs in a caterpillar; the hatched grubs 
feed on the living tissues; they make their way out 
eventually to begin a new phase of life, having 
killed their host. It is very difficult in such cases 
to avoid anthropomorphism. Perhaps it does not 
matter much to the caterpillar whether it is devoured 
from the inside or from the outside, and perhaps the 
ichneumon larve are rather beasts of prey than 
parasites. This, at least, is certain—that what the 
ichneumon insect does to the caterpillar is not so 
repulsive as what man often does to man, for man 
knows or ought to know what he is doing. The 
devilry, indeed, is all, unfortunately, with the man, 
for the icheumon’s behavior is the expression 
not so much of devilty as of a certain “ wildness ” 
