son 1950:397). Observations made on captive raccoons 
indicate that virgin females which become pseudopreg- 
nant have nipples indistinguishable from those of parous 
females. These animals may be distinguished from 
-parous females by the lack of placental scars in their 
uteri. Few of these animals are found in the wild; 
however, they do occur, and the only way they can be 
aeeated from the parous females is by an examina- 
tion of the uteri. During four recent fur seasons in 
‘Tilinois (1956-1959), uteri from 207 females that ap- 
peared to be parous on the basis of nipple development 
were examined, and 7 (3 per cent) had no placental 
scars. 
DISCUSSION 
Petrides (1959:249) reported that raccoons “in their 
first winter definitely can be identified as such where 
X rays of the distal ends of the radium and ulna dis- 
close the epiphyses to be distinct and not fused with the 
shafts of those bones. Animals in their second and 
subsequent winters have epiphyses joined with the di- 
aphyses.” Data presented in the present paper indicate 
that this conclusion needs modification for application 
in Illinois. Of the Illinois raccoons examined during 
hunting and trapping seasons, all individuals with 
broad epiphyseal plates were in their first winter except 
one female, and all those with no epiphyseal cartilage 
were 16-22 months of age or older; however, several 
animals 16-22 months of age, and some even older, had 
thin epiphyses, which presumably would place them in 
their first winter according to the finding of Petrides, 
who apparently did his research on Ohio raccoons. 
All male raccoons and 44 of 45 female raccoons 
with broad epiphyses were 15 months of age or younger 
at the time of examination, but 82 per cent of the males 
with thin epiphyses were 13-19 months of age and 61 
per cent of the females with thin epiphyses were 14-19 
months of age. Some males still retained thin epiphyses 
when 27 months of age, and one female with thin 
epiphyses was at least 42 months old. Presumably, all 
of these animals would be placed “in their first winter” 
by Petrides’ method of aging. 
The hunting and trapping season for raccoons in 
Illinois has been within the period October 15—January 
31 for the past several years. Many other midwestern 
states have open seasons covering approximately the 
same period. Because, in the northern half of Illinois, 
most raccoons are born in April and few, if any, earlier 
than March or later than June, table 1, the raccoons 
encountered here during the hunting and_ trapping 
season are either juveniles of about 4-10 months of age 
or adults 1 or more years older. No juveniles are more 
than 11 months old at the end of the hunting season. 
Rarely are adults less than 15.5 months old at the be- 
ginning of the hunting season. The earliest age at 
which broad epiphyses were found to disappear in 
northern Illinois raccoons was 13 months, tables 4 and 
5. The oldest age at which they were observed was, 
with one exception, 15 months, table 5. The exception, 
a female of 17 months, was parous, and her elongated 
nipples identified her as an adult. 
Thus, during the hunting and trapping season, the 
epiphyseal plates of the radii and ulnae give an almost 
infallible method for identifying northern Illinois rac- 
coons, both males and females, both living and dead 
animals, as juveniles or adults. With few exceptions, 
any raccoon found with broad epiphyses during the 
hunting and trapping season in the northern half of 
Illinois is a juvenile; any raccoon found without broad 
epiphyses is an adult. Examination of entire animals 
will help to eliminate the few incorrect age classifica- 
tions that might result if classification were based on 
epiphyses alone. 
Although the epiphyseal plates provide a_ useful 
method for aging both male and female raccoons, living 
or dead, in all but a few cases classification to juvenile 
or adult in dead males can be more easily accomplished 
by examining the bacula. 
Bacula from captive and from wild raccoons gener- 
ally showed similar rates of development, although there 
was considerable individual variation in size and con- 
formation, figs. 4-6. When the rate of development 
differed between captive and wild raccoons, the more 
rapid rate occurred in the captive animals. Perhaps 
the extra illumination and more nutritious diet given 
some males reared as pets are responsible for precocious 
sexual development and result in earlier development 
of the penis bone. Observations made on captive males 
indicate that those males which are sexually mature in 
their first year tend to have bacula which approach the 
adult condition. The penes of such males are extrusible 
at earlier ages than are those of males which are not 
sexually mature until nearly 2 years of age. 
In addition to affecting the development of the 
baculum, castration in males may delay closure of the 
epiphyseal cartilage slightly, but this delay is not as 
pronounced as the delay in the development of the 
baculum. Determination of the effects of castration on 
epiphyseal closure merits further study. 
The time of closure of epiphyses in females is close 
to that in males; however, epiphyseal closure occurs 
later in some females than in males or in other females, 
tables 4 and 5. Closure may be later in females that 
mate for the first time when approximately 10 months 
of age than in those that mate for the first time when 
approximately 22 months of age. Although some evi- 
dence supports this possibility, the data are insufficient 
to be conclusive. 
SUMMARY 
1. Several raccoons of known ages were kept in out- 
door cages and various characteristics associated with 
age were studied: body weight, degree of ossification 
of the epiphyseal cartilage of the radius and ulna, and, 
for the male, the size and the degree of ossification of 
the penis bone. 
