88 THE FIRST PRINCIPLES OF HEREDITY 



however, a satisfactory solution of the problem has been 

 found in accordance with our knowledge of the nuclear 

 character of hereditary transmission. It was shown 

 that what takes place in reality is a sort of double fertili- 

 zation. The pollen-grain divides into two generative 

 nuclei, one uniting with the ovum nucleus, forming the 

 embryo, the other fusing with the polar nuclei,* belonging 

 to the mother-tissue, and forming the protective and 

 nutritive layers around the embryo. 



I V. MA TERN A L IMPRESSIONS. 



It is a time-honoured belief that strong impressions made 

 on the mother whilst carrying will, in some mysterious way, 

 be imparted to the child, and evidence themselves in 

 strange birth-marks, malformations, etc. The mother may 

 have been frightened by a mouse : the baby born shows a 

 brown patch on the skin, having a vague resemblance to 

 the shape of a mouse, and the connection between both 

 facts is taken to be one of cause and effect. It is a true 

 post hoc, ergo propter hoc. There is no evidence whatever 

 that such cases are actually due to the mental experiences 

 of the mother during gestation. In most cases it is nothing 

 but a mere coincidence, because birth-marks are fairly 

 frequent, and strange experiences of pregnant women 

 also, especially when a malformation or other defect has to 

 be accounted for. Only striking coincidences, of course, 

 are noted, while the failures are forgotten. All we can say 

 is, that the mother's health has decidedly a general effect 

 on her offspring, and, further, in so far as mental experiences 

 may generally affect her own body, in so much may they 

 affect the foetus, which is a living part of her. But no cases 

 of special effects reproduced in the offspring can rationally 

 be accounted for, nor have such cases been scientifically 

 demonstrated. 



* The polar nuclei of the plant-embryo sac must not be confused 

 with the polar bodies of the maturation of the ovum. 



