REPAIR IN EVOLUTION 85 



scientific minimum. To say so much is not to deny that 

 small variations may finish, or polish, a rough incomplete 

 adaptation. From an eolith to the perfection of Chellean 

 art may be such a process, but the first eolith was no small 

 variation. 



The fact that the embryo acts upon the maternal 

 organism as a parasite against which the mother has to 

 be protected, is commonly recognized, but I have not seen 

 the obvious conclusion drawn that the whole history of 

 the mammal must have been due originally to a pathological 

 accident in some one or more of their ancestors. The 

 mammalian animal still lays eggs, but they are not ex- 

 truded. When such retention first took place, it must 

 have been due to an accidental pathological delay of the 

 travelling ovum, owing perhaps to catarrh of the tube. 

 Even now the mother has to be rendered immune to the 

 products of the offspring. Many of the phenomena of early 

 gestation are those of immunization, in some cases a very 

 slow process, as is shown in human beings by vomiting and 

 malaise. It has, moreover, not been clearly or generally 

 recognized, except by pathologists, that the very methods 

 by which the ovum attaches itself to the uterine wall are, so 

 far as the hostess is concerned, actually pathological and 

 bordering on the malignant. Yet they have resulted in a 

 series of protective reactions which save the parent and 

 permit the growth of the parasite. The method by which 

 the ovum becomes partially buried in the tissues is obviously 

 of a destructive kind, and curiously analogous to the 

 malignant processes seen in chorion-epithelioma. Bland- 

 Sutton remarks, "This disease is instructive because the 

 erosive action of the trophoblast is the physiological type 

 of the invasiveness so characteristic of many varieties of 

 cancer." It must, I think, be added, that it is the balance 



