414 Veterinary Obstetrics 



upon two conditions. First, the female must depart from the 

 physiologic rule that pregnancy inhibits ovulation and estrum. 



How frequently this rule is violated, we do not precisely know. 

 In the cow, especially the closely confined dairy cow, estrum 

 during pregnancy is by no means rare. Regular estrum may ap- 

 pear for two, three or more periods after fecundation, copulation 

 occur and, finally, a calf may be normally born from the first 

 copulation. We do not know, however, that ovulation occurs in 

 these cases. Perhaps it does. But superfetation rarely, if ever, 

 follows. 



A second essential condition is an open passage from the os 

 uteri externum, through one of the oviducts, to the pavillion of 

 the tube, so that the spermatozoa and ovum may meet. In uni- 

 para, this passage tends to become occluded early by the pres- 

 ence of a fetus in the uterine body and the adhesion of the fetal 

 membranes to the entire circumference of the tube. In bicornual 

 uteri, in which the fetuses are usually limited, in their location, to 

 the cornua, and the uterine body is vacant, the fetuses of the pri- 

 mary fertilization may be confined to one of the cornua, an open 

 avenue through the entire length of the other cornu exist and 

 a second fecundation at a more or less remote period occur. 

 De Bruin (Geburtshilfe b. d. Kleineren Haustieren) quoting 

 Kroon, relates that a goat was bred September 14, 1897, estrum 

 and copulation reccurring on November 5th, or 52 days later. 

 On February 13, 1898, 152 days after the first breeding, and at 

 the completion of the normal duration of pregnancy, she ex- 

 pelled two living and one dead, fully developed young. On 

 the following day, when the membranes were expelled, there 

 were discovered three more fetuses, perfectly formed, but 

 not fully developed. These Kroon regarded as certainly the re- 

 sult of the second copulation. 



Tapken, also quoted by De Bruin, observed superfetation in 

 sows. In one instance the sow was bred on February 22, 1890, 

 and again 17 days later. On June 21, 120 days from first breed- 

 ing, she' gave birth to 7 live pigs and, 14 days later, to 9 live and 

 3 dead pigs. 



The Wandering of Genital Cells. • 



Schmaltz (Carsten-Harms) claims that the spermatozoa may 

 pass through one of the oviducts, into the peritoneal cavity, 



