120 CALVIN P. STONE 



nosing about the body of the female the young animal discovers 

 the chief sources of secretions and excretions. Both males and 

 females begin to smell in the vaginal region when twenty-one to 

 twenty-three days of age (Licking, tables 2 to 11). 



The smelling lasts for only a few seconds until approximately 

 twenty-eight to thirty days of age, when the individual periods 

 of smelling lengthen somewhat and the total amount of smelling 

 during an observation is also increased by only a small amount 

 during the remainder of the prepuberal period. At the age of 

 thirty to thirty-five days, smelling is begun within a few seconds 

 after the female is placed in the cage. 



The amount of tune given to cage exploration is fairly con- 

 stant at various ages. This appears for the most part during the 

 last half of a ten to twelve minute period of observation. After 

 the young rat has thoroughly explored the female her presence 

 has less stimulating effect on it, hence it is more easily distracted 

 by stimuli coming from other sources noises in the room, odors 

 from the walls of the cage, loose shavings to be nibbled, feces, etc. 



Frequently the female, after making a tour of the cage, gives 

 her attention to the young in the cage for a short time. She 

 nibbles and licks his body and smells his genitals. This is done 

 at every age of the young male. The active females most fre- 

 quently stop to smell the genitals of the young. Sometimes the 

 two are seen smelling each other's genitals simultaneously. This 

 occurs most frequently when an adult male is placed with the 

 young animal. 



Attempts at nursing were seen during a few observation- 

 periods after the young animals were weaned. These attempts 

 consisted chiefly of sniffling and nibbling about the mammary 

 glands. 



In no case was a young male seen to launch a vicious attack 

 on an adult female. Being attacked, however, the young animal 

 sometimes defended himself. The adult female and adult male 

 showed practically no inclination to attack young animals under 

 forty days of age. Then, and until the observations were brought 

 to an end, the attacks of the adults were frequent. 



If attacked by a much larger animal the young rat seldom re- 

 sists by assuming the aggressive. He takes up a defense pose 



