HEREDITY 81 



egg-cell with which a male-cell has united in an orderly 

 and intimate way. This is the first great fact of heredity, 

 that each parent contributes the same amount of nuclear 

 material to the offspring. Another fact which is perhaps 

 more patent, is that the offspring is very like its kind. 

 No one denies that there is a general resemblance between 

 the offspring and its parents, but this resemblance may 

 descend even to minute details, and so we find, for 

 example, that malformations which were " natural " 

 to the parents may descend to the offspring. Then 

 there is another series of facts showing that the offspring 

 may reproduce characters that are not exhibited by the 

 parent, but were shown by some of the previous 

 ancestors. This " harking back " to the ancestral 

 characteristics, if it be very marked, is known as 

 atavism or reversion, and of this there may be several 

 degrees. 



Now every organism is usually slightly different from 

 its parents, and this is so much the case, that it is not 

 usual to have any difficulty in distinguishing it from 

 its fellow-offspring. That this difference is natural there 

 can be no doubt, for every organism begins life as the 

 result of the intimate union of two units of living matter 

 which may have had very different properties. 



Theories of heredity have been formulated at all times 

 and in all kinds of intellectual language. Of the majo- 

 rity of these we shall say nothing, limiting our remarks 

 to the most recent. 



With regard to this modern theory, there is much 

 controversy as to details, but the main fact stands out 

 clear, that there is an organic continuity of generations. 



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