THE LAWS OF HEREDITY 



terpreted by Professor Ernst Haeckel, when he 

 formulated his so-called "gastraea" theory, in 

 accordance with which each individual organism 

 tends, in the course of its development, to repro- 

 duce the ancestral forms through which the race 

 has passed in its evolutionary progress. 



Thus the human embryo is at first a single 

 cell and it passes in its embryonic development 

 through stages in which it resembles such lower 

 orders as fish and amphibia and lower mammals 

 before it assumes the proportions and character- 

 istics of the human being. 



The characters are, of course, slurred over, and 

 the reproduction of racial history is at best a 

 blurred and epitomized one, yet the fact that the 

 embryo does pass through such varied transfor- 

 mations, and that these at least roughly outline 

 the racial history, is a highly interesting and im- 

 portant one, and may be said to exemplify the 

 fundamental law of heredity in the most com- 

 prehensive way. 



It is obviously a mere detail within this gen- 

 eral law that an adult individual should some- 

 times develop a characteristic or an anomaly of 

 some organ or tissue at the same age when the 

 same characteristic or anomaly was manifested 

 by a parent. Examples in point are furnished by 

 those not familiar cases in which a cancerous 

 growth develops at about the same age in parent 

 and offspring, or in which a mental aberration 

 similarly manifests itself. 



Such manifestations of heredity are spoken of 

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