APPENDIX II 



embryos thus misplaced grew, attached themselves to the 

 mesenteries or elsewhere on the peritoneal lining of the 

 abdominal cavity, and lived out the full term of gestation. 



The distinguished French biologist Robert Courrier in his 

 Endocrinologie de la Gestation (Paris, 1945) reports a 

 curious observation upon a rabbit in which, on the 19th day 

 of pregnancy, one embryo was caused by surgical means to 

 escape from the uterus into the abdominal cavity, where it 

 attached itself to the peritoneum. Two other embryos were al- 

 lowed to remain in the uterus. The ovaries were removed at 

 this same operation. At the end of the usual term of gestation, 

 the fetus in the abdominal cavity was alive, whereas those left 

 in the uterus had died as a result of the loss of the ovaries. 

 Evidently the corpora lutea are essential for the welfare of 

 the embryos only if the latter are in the uterus. 



We must assume from such experiments that the early 

 mammalian embryo has a strong inherent vitality which will 

 enable it to grow wherever it has the necessary warmth, a 

 supply of oxygen and nutritive materials, and a generally 

 suitable chemico-physical environment. Since, on the other 

 hand, as experiments have proved, the early embryo cannot 

 survive in the uterus except under the influence of pro- 

 gestational changes induced by the corpus luteum, it follows 

 that the uterus, when not so prepared, is actually an un- 

 favorable place for the early embryo as compared with the 

 anterior chamber of the eye, the peritoneal cavity, or even a 

 tissue-culture slide. 



This seemingly paradoxical situation is made intelligible 

 by thinking of the evolutionary background of mammalian re- 

 production. It is characteristic of eggs and early embryos of 

 lower animals that they are prepared to develop without 

 shelter and nutriment from the mother. When the mammals 

 evolved the phenomenon of utero-gestation, the chosen place 

 of shelter, the uterus, was developed from part of the ovi- 

 duct, a channel that had for its purpose the efficient trans- 

 portation and discharge of the eggs, not their retention and 



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