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BULLETIN OF THE BUREAU OF FISHERIES 
about the middle of the body. The intestine bends so as to return forward for a 
distance and then curves backward to continue its course to the vent. From this 
time on the intestine continues to increase in length rapidly, the coils lying chiefly 
on the right side of the body and taking the form of a circle. 
Fig. 48. — Digestive tract of a 9H-incb adult, with fat 
and liver removed to show its coiling, viewed from the 
right side 
When the fish is 17 millimeters in length the entire digestive tract equals the 
length of the fish; at 24 millimeters it equals nearly twice its length; while adult 
specimens 6 to 12 inches long show that it falls little short of being as great as three 
times the fish’s length. 
DETERMINATION OF AGE 
RELATION BETWEEN GROWTH OF SCALES AND SIZE OF FISH 
The scale of the white sucker is of the cycloid type. While circular or elliptical 
the first two years, it gradually assumes a quadrilateral form, developing straight 
sides and a rounding base and apex. The focus is centrally located, though nearer 
the posterior edge during the first year or two. In about 30 per cent of the scales 
examined the focal area showed very irregular markings. Instead of concentric 
circuli, a reticulium of ridges had been developed. Such scales are not useful in 
age determination, though reported by nearly all authors and of wide distribution 
among species. 
In this species the radii are confined principally to the anterior and posterior 
quadrants, very few being truly lateral. They seldom if ever branch, and but a 
small percentage fails to extend the whole way from edge to focus. Nothing of 
value resulted frAm a careful count of radii in about 200 scales taken from specimens 
from 28 to 250 millimeters body length. While the furrows are very shallow in 
young scales they are deeper and straighter in larger ones and maintain the clear 
appearance characteristic of the newly formed margin of the upper surface of the 
scale. 
The circuli are fine, narrow, parallel ridges, separating relatively wider furrows. 
They are concentric and nearly always parallel with the true edge of the scale. If 
they run obliquely to the edge they always do so along the sides of the scales. Their 
distance from one another varies with the time of year but averages about one 
twenty-fifth of a millimeter. 
