XXVI 
THE PROBLEM OF PARASITISM 
NE of the perplexing shadows in the pleasant 
picture of animate nature is the frequency 
of parasitism. To some minds it appears as a blot 
spoiling the whole script. But without denying 
that there is some warrant for practical, zsthetic, 
and ethical recoil, we think that much of this is due 
to lack of perspective. Let us take a rapid survey 
of the facts. Thousands of living creatures, both 
plants and animals, live in or on others, bound 
up with them in a brutally direct nutritive depend- 
ence and incapable of living in any other way. 
Uninvited non-paying boarders they are, who 
make their hosts no return for the hospitality 
enjoyed. When we think of the “ minor horrors of 
war,” regarding which Dr. Shipley has written so 
admirably, of yard-long tapeworms and plump 
maw-worms in their inglorious life of ease, of mites 
and ticks innumerable, of fish-lice and flukes, of 
rusts and mildews and other parasitic fungi, and 
so on down to the microscopically minute bacilli 
and trypanosomes, we are appalled at the number 
and diversity of parasites. It is some relief to find 
that no backboned animals are parasitic unless it 
be the hags (Myxine) which sometimes burrow 
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