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 lieing insects, and one-tliird of 

 these of terrestrial species, and ten per cent, being crustaceans; 

 that one-fourth consisted of vegetation, about equally aquatic and 

 terrestrial, and that tlie remainder is nuid, probably containing 

 more or less liuid orcfanic matter. 



Comparison of the Guours. 



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 first 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 lengtii, 

 mud was still abundant, but much less so than in the first, aver- 

 asfinsf less than half the whole. If we exclude this indiirestible 

 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 sixrnificance. 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 larvie greatly predominant in the first 

 group, making one-fourth of tlieir food, and Chironomus larvae 

 in the second amounting to sixteen per cent. The second of 



