34 STRUGGLE AMONGST ANIMALS 



but even under conditions with which I am so 

 familiar as those in the Gardens here, I cannot be 

 certain what are the causes of the preferences. Still 

 less is it possible to guess why onentalis should have 

 spread from the far east and have become quite com- 

 mon in Germany although there was already a cock- 

 roach in possession ; why it should be most abundant 

 in England, and reaching America, be common, 

 although less abundant there ; or why the German 

 cockroach should establish itself in England, on the 

 whole less successfully than the oriental form, and 

 yet on reaching America become the most abundant 

 there. Still less can we guess why cockroaches should 

 on the whole have displaced the domestic cricket. 

 But at the least we can be certain that in this com- 

 paratively recent and well-observed set of changes 

 in the distribution of species, there is nothing even 

 remotely comparable with the interpretation of the 

 struggle for existence as war. 



It is unnecessary to multiply instances. The 

 causes of the success of one or another species in the 

 struggle for life cannot be associated with any cir- 

 cumstances that suggest the active violence of the 

 members of the successful species directed against the 

 members of the less successful species. Recently I 

 have been reading a patient and exact study of 

 nature of a kind that would have delighted Darwin. 

 Dr. Victor Shelford, of the Department of Zoology 

 in the University of Chicago, with a number of 

 assistants, has been engaged for years in making a 

 complete survey of all the animals, large and small, 

 that live in a limited area near Chicago, and has pub- 

 lished his results in a volume under the title Animal 



