The Food of the Smaller Fresh- Water Fishes. 
91 
Summing up, in a word, the characteristics of the food of the fami- 
ly as thus indicated, we may say that about one-half of it consists 
of animal substances, one-third being insects, and one-third of 
these of terrestrial species, and ten per cent, being crustaceans; 
that one-fourth consisted of vegetation, about equally aquatic and 
terrestrial, and that the remainder is mud, probably containing 
more or less fluid organic matter. 
Comparison of the Groups. 
It will be remembered that the groups were based upon differ- 
ences in the structures relating to the appropriation and mastica- 
tion of food. It is consequently from a comparison of the ratios 
of these groups that we shall derive the most interesting facts 
relating to the correspondence of food and structure. The most 
conspicuous result is the great preponderance of mud in the 
intestines of the fishes of the group, characterized by an extra- 
ordinarily elongate intestine, and by pharyngeal teeth destitute 
♦of hooks and provided with a broad grinding surface. Here, as 
already noted, mud, sand, and gravel amounted to about three- 
fourths of the matter ingested, while in the third and fourth groups 
only trivial and accidental quantities occurred. In the second 
group, on the other hand, with intestines intermediate in length, 
mud was still abundant, but much less so than in the first, aver- 
aging less than half the whole. If we exclude this indigestible 
matter, however, we shall find the first group still further distin- 
guished by the predominance of vegetation as compared with 
animal matter, the latter being only about one-third the former, 
while in Groups III and IV, on the other hand, vegetation 
amounts to about one-third the animal food. The groups last 
mentioned, distinguished from each other as they are, only by the 
presence of a masticatory surface on the pharyngeal teeth in the 
first, and its absence in the second, differ scarcely at all in their 
general food characters, and this structural feature seems therefore 
to be of little significance. In both the animal ratio amounts to 
seventy-five per cent., and vegetation stands in each at twenty- 
five; while insects are respectively fifty and sixty-one. It is true 
that we find neuropterous larvae greatly predominant in the first 
group, making one-fourth of their food, and Chironomus larvae 
in the second amounting to sixteen per cent. The second of 
