20 
The Food of Fishes. 
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 de- 
pends 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 
construction 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 mechan- 
ism of the aquatic life of the locality, both animal and 
vegetable, of which his species forms but a single ele- 
ment.* 
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 great- 
est 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 subject of peculiar interest and 
value. It includes many of the most important relations 
* I cannot 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 working 
knowledge of those parts of it which chiefly attract popular attention, 
—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 organic 
unit, must study it in action, and direct principal attention to the laws 
of its activity. 
