204 SECRETS OF ANIMAL LIFE 



what is for it simply a new and very promise ful 

 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 larvae 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 devilry as of a certain " wildness " 



