228 CHARLES U. STOCKARD AND G. N. PAPANICOLAOU 



frequently by such studies that ovulation takes place a few 

 hours after parturition, the female accepting the male at that 

 time. These facts are generally admitted but the most varied 

 opinions prevail regarding the times of the su})se(iuent ovulations, 

 when conception does not occur soon after parturition. 



The question whether ovulation in the guinea-pig is spontane- 

 ous or dependent upon copulation has often been raised by vari- 

 ous workers. The majority are of the opinion that ovulation is, 

 or may be, spontaneous although influenced by copulation, and 

 that there is no definite regularity or typical periodicity in the 

 ovulation cycles. 



Bischoff, was one of the oldest advocates of the theory of spon- 

 taneous ovulation. In a special paper devoted to the study of 

 this problem in 1844, and later in a study of the development of 

 the guinea-pig ('52), he defended the view^ that the guinea-pig, 

 hke all other mammals, has a spontaneous ovulation. Bischoff 

 states that the mature eggs reach the oviducts through the rup- 

 ture of the greatly distended Graafian follicles during the first 

 twenty-four hours following parturition. This fact, he points out, 

 had previously been observed and was generally accepted by the 

 earlier investigators with the exception of Schulz, 1829, who 

 failed to recognize a heat period before the fifteenth day after 

 parturition, and sometimes even to the forty-ninth day. 



According to Bischoff copulation takes place within three hours 

 after parturition. He agrees with the earlier statements of 

 Aldrorandi, Legullois, Fraser and Schultz regarding the length 

 of gestation, or period of pregnancy, as being about nine weeks, 

 which is very nearly correct, sixty-two days being the normal 

 length of time. He held that the return of the heat period did 

 not follow any regular periodicity: "Wenn die Befruchtung 

 unmittelbar nach der Geburt verhindert wird, so scheint die 

 Wiederkehr der Brunst an keine ganz bestimmte zeit geknlipft 

 zu sein, sondern von Umstanden der Individualitat, des Alters, 

 der Jahreszeit, der Fiitterung, etc., abzuhangen." In fom* 

 cases in which the females were prevented from copulating for 

 some time after they gave birth to young a copulation occurred 

 40, 50, 51 and 51 days after the birth. 



