depart, the female came out of the burrow and 
smelled the earth where male 12 had been rolling. 
As she was doing this he returned and they touched 
noses. The activity was terminated when all the 
rats in the pen became startled from some unknown 
cause. At the age of 94 days she was seen to 
engage in extensive wanderings through the East 
Alley and Area II. Upon leaving Area II by 
way of Passage 2 she apparently heard adult male 
8 who was grooming himself about 15 feet away 
against the outside barrier fence. She turned 
around and went over to him, whereupon he 
inspected her genital region and there ensued a 
sexual chase. She was known to have conceived 
that night. Nine days later one of her brothers 
kept attempting to mount her as she was departing 
from the Food Pen. These attempted mounts 
were made while she was in motion. Intermittently 
she stopped and pawed him away with her forefeet. 
This is a typical behavior of a female who though 
still sexually attractive to males, is herself not 
receptive. 
The general impression that I have gotten from 
these observations is that subadults between the 
ages of 80 and 115 days engage in sexual behavior 
less frequently than do adults; that sexual behavior 
which they do engage in is less complete or less 
intense; and thay they are more likely to engage 
in sexual behavior with an adult than with another 
subadult. This latter is quite similar to the 
situation in which subadults rarely fight effectively 
among themselves, but rather experience aggres- 
sive social conditioning by interacting with adults. 
The time sequence of some of the maturational 
phenomena are diagra mmatically shown in figure 
103. 
3. Sexual Behavior and Reproduction 
A. Sexual Behavior. There are certain behaviors, 
which, though not necessarily of sexual implica- 
tion, form the background for the full expression 
of sexual behavior. One of these is the habit of 
one rat closely following another. Its origin may 
AGE IN DAYS FROM BIRTH 
0 10 20 30 40 50 60 70 80 90 100 110 120 
1 1 1 1 1 1 1 1 i i t i r i i i i i i i i i i i r 
SQUEAK WHEN DISTURBED 
M ERUPTION OF DORSAL HAIR FOLLICLES 
he -^TRANSPORTATION BY MOTHER 
K *EYES BEGIN TO OPEN 
he-H EXPLORATIONS OUT OFNEST-BUT WITHIN BURROW 
N — H INITIAL EXPLORATIONS ON SURFACE -BUT NEAR HOME BURROW 
W-H FIRST EXTENSIVE WANDERING- INCOMPLETE FOOD TRANSPORT 
he ^TERMINATION OF NURSING MOTHER 
he N FIRST HARBORING AWAY FROM SIBS OR MOTHER 
he X CLOSE BOND WITH MOTHER- THEY FOLLOW HER 
SIBS HARBOR TOGETHER -AWAY FROM 
* *H0ME BURROW-MOST OF TIME 
, _ _ .SOCIAL ADJUSTMENTS WITH ADULTS- 
K *IN WHICH ADULTS ARE RELATIVELY 
TOLERANT 
he 
I. BEGINNING ADULT SEXUAL BEHAVIOR 
2 LOSS OF JUVENILE PELAGE 
3. MARKED ANTAGONISTIC RELATIONS 
WITH OLDER RATS 
Figure 103. — The time sequence of some maturational phenomena from birth to the beginning of adult sexual behavior. 
152 
