100 CALVIN P. STONE 



growth appearing prior to the age of sexual maturity. Males 

 were separated from females at weaning time. All were segre- 

 gated for observation in wire-mesh cages which rested on one- 

 half inch of wood shavings contained in galvanized-iron trays. 

 When not in observation cages, all animals except those used in 

 experiments involving isolation, were permitted to mingle freely 

 with others of the same sex and of approximately the same age. 

 Individuals kept in isolation were confined in cages of the di- 

 mensions 12 by 8 by 8 inches. 



Feeding hours were regular and fell daily between 6.00 and 

 8.00 p.m. The diet, uniform throughout the period of study, 

 consisted of white bread and whole milk served together in small 

 tin containers during six days of the week. On the remaining 

 day a grain mixture (McCallum diet), made into a mash by the 

 addition of water, was substituted for the bread and milk. Once 

 a week fresh cabbage leaves were added to the above diet. 

 Weight records were taken at five-day intervals or oftener in 

 experiments requiring more detailed records of weight. 



The animals whose sexual behavior was observed from day to 

 day were removed from the housing cages to individual observa- 

 tion cages (12 by 8 by 8 inches) from four to six hours prior to 

 the tune of observation. The purpose of isolating the animals 

 was to allow time for each to become thoroughly cage-adapted, 

 thereby reducing random cage exploration to a minimum during 

 the period of observation. 



In general, the method of studying the sexual behavior of the 

 young animals was systematic observation of normal and oper- 

 ated animals in confinement. Special methods and technique 

 employed in particular phases of the work will be described in 

 detail in connection with the report of experimental data in the 

 following sections of the paper. 



THE COPULATORY ACT 



The constituent elements of the copulatory act are well co- 

 ordinated at the time of the initial copulation. No more funda- 

 mental problem confronts the student of animal behavior than 

 that of discovering the process by which these constituent ele- 



