136 THE PHYSIOLOGY OF REPRODUCTION 



the peritoneum is used as a common envelope for the ovary and the 

 end of the tube. Thus in the dog and ferret the ovary is enclosed 

 in a sac communicating with the cavity of the tube, so that the 

 discharged ova can scarcely fail to effect an entrance into the uterus. 

 There can be little doubt, however, that in the majority of animals 

 ciliary movement plays an important part in directing the course of 

 the expelled ova. 



Nussbaum * has described the eggs of the frog as being carried 

 into the mouths of the oviducts by the motion of the cilia of the 

 crclomic epithelium. These cilia are said to drive in a forward 

 direction any small bodies lying free in the coalom. Harper 2 states 

 that in the pigeon the egg is clasped by the oviduct, which at this 

 time displays active peristaltic contractions, as if in the act of 

 swallowing the egg. 



There is evidence, however, that ova which are discharged from 

 one ovary do not always pass into the oviduct on .the corresponding 

 side. For example, instances have been known of animals with a 

 bicornuate uterus becoming pregnant in the uterine horn on the 

 side opposite to that on w r hich the ovary had discharged (as indicated 

 by the presence of a newly formed corpus luteum). Moreover, it 

 has been recorded that animals from which one ovary had been 

 removed have become pregnant in the uterine horn of the other 

 side, an observation which indicates that the ova which are discharged 

 from one ovary may travel across the peritoneal cavity and enter 

 the Fallopian tube which was connected with the other ovary. 3 



It has been stated that in certain abnormal cases an ovum which 

 escapes altogether into the peritoneal cavity may yet become fertilised, 

 bringing about a condition of abdominal pregnancy. There can be 

 little doubt, however, that abdominal pregnancy is nearly always 

 secondary to tubal pregnancy, and that primary ectopic pregnancy 

 is exceedingly rare. According to Loeb 4 the uterine mucosa is the 

 only form of tissue which is able to produce a decidua in the guinea- 

 pig, and while an ovum in the body cavity may undergo the early 

 stages of development, lack of the proper response on the part of the 

 host-tissue (lack of decidual reaction) renders development of the 

 later stages of extra-uterine growth impossible Blair Bell, 5 however, 



1 Nussbaum, "Zur Mechanik der Eiablage bei Rana fusca" Arch. f. Mikr. 

 Anat., vol. xlvi., 1895. 2 Harper, loc. cit. 



3 Cf. Hammond, "On some Factors Controlling Fertility in Domestic 

 Animals," Jour. Agric. Science, vol. vi., 1914 (for rabbits and pigs), and Corner, 

 "The Corpus Luteum of Pregnancy as it is in Swine," Contribution* to 

 Embryology, vol. ii., Carnegie Institute Pub., 1915. Internal migration of ova 

 from one uterine horn to another has been shown to be not uncommon. 



* Loeb (L.), " The Experimental Production of an Early Stage of Extrauterine 

 Pregnancy," Pnx-. Av<e. Exp. ttiol. 3/ed., vol. xi., 1914. 



5 Blair Bell, '" Primary Abdominal Pregnancy in a Rabbit," Proc. Roy. Soc. 

 Ned., 1911. 



