WHITE SUCKER 
163 
A single section, 10 microns thick, shows as many as 18. How many occur on 
the lips of an adult fish is problematical, but as 576 macroscopic papillse may be 
found on a 12-inch specimen, and as each of these contains at least a score of taste 
buds, the total number must be over 10,000. The writer is inclined to think that the 
eyes, due to their location, play a small part in locating the food, and that the sense 
of taste is very effective in locating the food. 
Fig. 32. — Longitudinal section of the head of a 16-millimeter 
specimen showing descent of the mouth, division of the 
nasal pit, and increase of the taste papillse in the pharynx 
Fig. 34. — 12J4 millimeters 
Fig. 35.— 14 millimeters 
Descent of the mouth, division of the nasal pits, and appearance of the labial papillse, as seen in a series of anterior views 
of the developing sucker. 
HISTOLOGY OF THE INTESTINE 
A few words upon the development of the remainder of the digestive tract may 
not be out of place here. The stages preceeding and after the metamorphosis of 
the mouth and the sudden lengthening of the intestine are of special interest. 
Conditions at hatching have been described. By the time the larva is 11 milli- 
meters in length the yolk sac has disappeared entirely and the liver and air bladder 
