area of the muscle is particularly large and flat in 
cross section, Fig. 10B and D, and the extent to which 
it can be readily everted usually distinguishes females 
of this age class from yearling females, Fig. LOA and 
C.. 
The Bursa of Fabricius.—Use of the bursa of 
Fabricius to distinguish immature from older water- 
fowl has been described, with reference to ducks, by 
Gower (1939:427) and by Hochbaum (1942:304-306 ) 
and, to Canada geese, by Elder (1946:106-108 ). Be- 
cause Canada geese require a longer period to become 
sexually mature than do most common species of ducks, 
the bursa of Fabricius is a useful age criterion for 
distinguishing yearling geese, in winter, from sexually 
mature adults (Hanson 1949:179-180). 
The depth of the bursa in immatures ranges be- 
tween 24 and 35 mm. The average is about 27 mm. 
In yearlings, it varies between 15 and 24 mm and 
averages about 20 mm. The bursa is either closed or 
has been resorbed in approximately 58 percent of 
geese in their third winter of life; the remainder have 
a bursal depth varying from 17-21 mm and an aver- 
age depth of 15 mm. Penis characters must be es- 
pecially carefully evaluated in aging these males. As a 
criterion of age in Canada geese, the bursa is of value 
chiefly in separating yearling from older geese, but it 
must be used in combination with other cloacal char- 
acters. Absence of the bursa can be considered quite 
certain evidence that a goose is 24 or more years of 
age. 
Closure of the bursal opening into the proctodeum 
of the cloaca apparently proceeds most rapidly during 
the second year of life, that is, in the age group achiey- 
ing sexual maturity in the third spring of life. A fe- 
male, Fig. 6A, shot along the Sutton River, Ontario, 
near the coast of Hudson Bay in early June and judged 
to be nesting for the first time, had a clutch of three 
eggs, a very restricted incubation patch, and a bursa 
that had membranous walls that could be probed only 
with difficulty. She was judged to be nearly 2 years of 
age. 
The Oviduct.—In female Canada geese, the mem- 
brane that occludes the opening of the oviduct into 
the cloaca is usually not resorbed until after the geese 
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Fig. 11.— Penis of, A, an immature Canada goose during the first winter of life; B, a yearling during its second winter 
of life; and, C, an older adult in winter. The stage of development the penis a yearling, D, attains during its second spring 
of life (an immature the previous winter) is nearly comparable to that attained by an adult, E, 
in spring. 
