78 The Food of the Smaller Fresh- Water Fishes. 
It is distinguished from all other species by the great length of 
the intestine, which is from six to nine times the length of the 
body, and is spirally coiled about the air bladder. The gill-rakers 
are numerous, about twenty in number to each gill, but are very 
short, scarcely projecting beyond the anterior margin of the arch. 
They are evidently almost totally inefficient as a straining appa- 
ratus. 
Of the great number of specimens available for dissection, only 
nine were studied, since the contents of the intestines were found 
so uniform in character that it was not deemed worth while to 
multiply instances. These were from both extremes and also 
from the center of the State, but were all taken in July, August 
and September. The intestine was invariably filled from end to 
end with a black and slimy matter, which, when examined under 
the microscope, was found to consist almost wholly of fine mud. 
When the intestine was emptied and the contents stirred up in 
alcohol and repeatedly decanted so as to separate the coarser frag- 
ments, the organic matter was easily distinguished. It made on 
an average, only about one-fourth of the contents of the intestine, 
the remainder consisting of the finest particles of sand and clay. 
Not far from one-fifth of the whole amount was of vegetable ori- 
o 
gin, consisting chiefly of filamentous Algae, mingled with a few 
diatoms, but comprising occasionally minute fragments of other 
kinds of vegetation also. The only animal objects noted were 
occasional Chironomus larvae and Diffluma. Sometimes the intes- 
tine was wholly filled with almost pure mud, in which no organic 
structures whatever could be detected. Date and locality seemed 
to make no material difference in the food of this fish, which 
should evidently be classed as limophagous. The ratios of ani- 
mal to vegetable food were scarcely different from what one would 
expect to find in the intestine of a fish which had the habit of 
swallowing mud rich in organic matter, the greater ratios of vege- 
tation being apparently due to the fact that plants are more abun- 
dant in the water than animals. 
PlMEPHALES PROMELAS, Raf. BLACK HEAD. 
This species is generally distributed throughout Central and 
Northern Illinois, but is not very abundant. We have taken it 
only in rivers and larger creeks, but have not found it south of 
Jersey County. 
