20 ^ The Food of Fishes. 



isfactory understanding of any part. If one wishes to be- 

 come acquainted with the black bass, for example, he will 

 learn but little if he limits himself to that species. He 

 must evidently study also, the species upon which it depends 

 for its existence, and the various conditions upon which 

 these depend. He must likewise study the species with 

 which it comes in competition, and the entire system of 

 conditions affecting their prosperity. Leaving out any of 

 these, he is like one who undertakes to make out the con- 

 struction of a watch, but overlooks one wheel; and by the 

 time he has studied all these sufficiently, he will find that 

 he has run through the whole complicated mechanism of 

 the aquatic life of the locality, both animal and vegetable, 

 of which his species forms but a single element.* 



In such a general survey of the plants and animals of a 

 region, the study of their food relations will be found to 

 afford an admirable objective point. Doubtless, of all the 

 features of the environment of an individual, none affect 

 it at the same time so powerfully, so variously and so in- 

 timately as the elements of its food. Even climate, sea- 

 son, soil, and the inorganic circumstances generally, influ- 

 ence an animal through its food quite as much as by their 

 direct action. It is through the food relation that animals 

 touch each other and the surrounding world at the greatest 

 number of points, here they crowd upon each other the 

 most closely, at this point the struggle for existence becomes 

 sharpest and most deadly ; and, finally, it is through the food 

 relation almost entirely that animals are brought in contact 

 with the material interests of man. Both for the student 

 of science and for the economist, therefore, we find this sub- 

 ject of peculiar interest and value. It, includes many of 

 the most important relations of a species, and may prop- 



*I can not too strongly emphasize the fact — frequently illustrated, I 

 venture to hope, by the papers of this series — that a comprehensive sur- 

 vey of our entire natural history is absolutely essential to a good work- 

 ing knowledge oi those parts of it which chiefly attract popular atten- 

 tion,— that is, its edible fishes, its injurious and beneficial insects, and 

 its parasitic plants. Such a survey, however, should not stop with a 

 study of the dead forms of Nature, ending in mere lists and descriptions. 

 To have an applicable value, it must treat the life of the region as an or- 

 ganic unit, must study it in action, and direct principal attention to the 

 laws of its activity. 



