106 CALVIN P. STONE 



available was placed in the cage with a male. The young 

 animals were observed individually, upon the introduction of 

 the female, for periods varying from five to fifteen minutes daily, 

 or longer if the activity of the young animals made a prolonged 

 period of observation desirable. Notes pertaining to the general 

 types of activity, the aggressiveness or lethargy of male or fe- 

 male, etc., were made. Also points of a more specific nature 

 were looked for, such as: smelling and licking the ano-vaginal 

 zone; attempts at sticking; nibbling at the sheath of the penis; 

 unsheathing, licking and manipulating the penis; rhythmic ex- 

 trusion and retraction of the penis in the sheath; mounting and 

 palpation of the female sides while in the copulatory position; 

 playful attempts at copulation prior to the age of sexual maturity. 



In the second series of observations the method was varied 

 to bring out more details on certain points not revealed in the 

 previous study. In the first series quantitative data concerning 

 the kinds of activities and their duration were not secured. Fur- 

 thermore, there was no control over the activities aroused by 

 mingling with other animals of the same age while not under 

 observation. 



In the second series 8 animals, 6 males and 2 females, all of 

 the same litter, were used. It was a well nourished litter and 

 the young were able to subsist on a bread and milk diet at the age 

 of twenty days. When twenty-one days of age the young were 

 weaned and isolated in individual cages where they were kept 

 during the entire period of study. Under these conditions they 

 had no opportunity to mingle with other animals, except while 

 with the adult during the period of observation. On alternate 

 days the behavior of each animal was studied and records were 

 made which gave the type of activity and its duration in each 

 minute of a twelve-minute period. 



A simple scheme for recording the behavior was devised. 

 All the types of activity that had been observed during the first 

 study were listed. Certain acts of a similar nature were thrown 

 together in order to reduce the number of categories as much as 

 possible, yet keeping separate all acts of a doubtful or definitely 

 sexual nature. Obviously this catalogue is devoid of logical 



