SEXUAL CYCLE OF THE GUINEA PIG. 



239 



I may state that at this penod a slightly transparent serous 

 or a turbid or viscid secretion can be noticed; but within 2 or 3 

 days this will disappear, and the swelling of the external organ 

 will cease and normal conditions will again prevail. 



PHENOMENA OF FIRST MENSTRUATION OR HEAT PERIOD IN THE 



GUINEA PIG. 



The first heat or menstruation of the guinea pig differs in some 

 respects from the later periods of heat. The symptoms of 

 prooestrum are of much longer duration. While as stated above, 

 the normal prooestrum lasts about I to 1^2 days, during the 

 first menstruation a slight secretion and swelling continues for 

 3 to 8 days; only then appears the period of heat proper. In 

 some instances the secretion and swelling disappear temporarily. 

 Then a few days later it begins again and now develops into the 

 regular heat. As stated, generally the duration of the procestrum 

 is variable and usually longer in the first menstrual period. 



DICESTRUS PERIOD OF THE GUINEA PIG. 



The dioestrus period is the length of time between two consecu- 

 tive menstruations or heat periods. Through observation of the 

 condition of heat we determined the length of the sexual cycle in 

 the guinea pig; we used for this purpose a considerably larger 

 material than Loeb 1 and Stockard and Papanicoloau 2 used in 

 their observations. While our average agrees with that of the 

 aforementioned authors, we found a greater range of variation 

 than Stockard and Papanicolaou. From the observations of 

 Loeb it follows that in some exceptional cases the period may be 

 even shorter than that found by us. 



From these figures we may conclude that the average duration 

 of this period was 15 to 16^2 days. I found that where the 

 length of time was decidely shorter (14.1/2 days) or longer (17 to 



1 Leo Loeb, BIOLOGICAL BULLETIN, 1914, XXVII. , i. 



2 C. R. Stockard and G. Papanicolaou, Am. Jour. Anat., 1917, XXII., 225. 



