SEXUAL CYCLE OF THE GUINEA PIG. 24! 



which both are lacking on the other hand. Therefore the male 

 attempts copulation only in the former case. When a number 

 of animals of both sexes are together and among them is a 

 female in the heat period, the males run around and search for 

 that particular female, ultimately finding it. 



I am convinced from this searching of the male for the female 

 in heat that he is led to do so by a special odor characteristic of 

 the female, when it reaches the heat period. This peculiarity 

 is common to the mouse, the rat and the rabbit. 



Influence of Food upon the Character of Heat and on the Time 

 when Sexual Maturity is Reached. 



The vigor of the heat in guinea pigs depends upon the nourish- 

 ment which the animals have received. Guinea pigs which had 

 been poorly fed develop weak heat. This applies to the duration 

 of the heat as well as to the vigor of the symptoms. The length 

 of the dicestral period does on the other hand not seem to be 

 affected by the state of nourishment. 



I made observations on the influence of food on the time when 

 sexual maturity is reached. 



I. On especially prepared rich food the first heat was observed 

 45 to 60 days after birth. 



II. On usual food 55 to 70 days after birth. 



III. On food of poor quality 75 to 100 days after birth. 



The usual food consisted of hay (or grass), carrots (or beets) 

 and oats. In the rich diet corn cake was added, while the poor 

 diet consisted merely of hay (or green grass) and oats. When 

 the quality of the food was above the ordinary, its effect on the 

 size of the guinea pig as well as their physical condition in other 

 respects could be seen. They were of the average condition, 

 when ordinary food was given at regular intervals, and the poorly 

 fed animals were poorly developed physically. The food is 

 therefore of the greatest importance as far as the time of sexual 

 maturity and the character of the heat are concerned. 



Influence of Climate on the Character of the Heat and the Length 



of Sexual Cycle in the Guinea Pig. 



The extreme temperature of the summer months (a tempera- 

 ture of over 90 F. in Granby, Mass.) has a weakening effect on 



