SEXUAL CYCLE OF THE GUINEA PIG. 



245 



The following table shows the length of time necessary for the 

 symphysis pubis to return to its normal condition following labor : 



Time when the Symphysis Pubis has again 

 Become Normal Following Labor. 



From these data we may conclude that the separation of the 

 symphysis pubis begins from 5 to -7 days previous to birth, or 

 from the 6ist to the 63d day after copulation. Under ordinary 

 conditions birth should not take place before the 5th day following 

 this separation. The length of the period of gestation should 

 therefore usually be 68 days. 



Preparation for Labor. 



In the guinea pig the separation of the symphysis pubis 

 serves as a preparation for parturition, inasmuch as the orifice 

 of the normal pelvis is too narrow to permit birth to take place. 

 Moreover we find at the same time the same remarkable softness 

 and elasticity of the muscles and joints as during the ordinary 

 menstrual period. This same effect (emanating from the ovary 

 or pituitary gland) I have also noticed in the rat and in the 

 rabbit and I presume it is the same in all mammals. 



The Time of the First Heat in the Puerperium. 



The time of the beginning of heat in the period directly follow- 

 ing labor is somewhat variable. In 20 guinea pigs in which 

 parturition set in at the normal time (67 to 69 days after copula- 

 tion) I found the following figures : 



Beginning Puerperal Heat After Parturition. 



