1900.] on Facts of Inheritance. 347 



narrow a sense, I should say that precision of observation and record 

 which admits of statistical, mathematical, or some other exact formu- 

 lation. While nothing can take the place of experiment — which is 

 urgently needed for the further development of our knowledge of 

 heredity — much has been gained by the application of statistical and 

 mathematical methods to biological results — a new contact between 

 different disciplines — which we may particularly associate with the 

 names of Mr. Francis Ualton and Mr. Karl Pearson. 



I. The Physical Basis of Inheritance. 



"What was for so long quite hidden from inquiring minds, or but 

 dimly discerned by a few, is now one of the most marvellous of 

 biological commonplaces — that the individual life of the great majority 

 of plants and animals begins in the union of two minute elements — 

 the sperm-cell and the egg-cell. These microscopic individualities 

 unite to form a new individuality, a potential offspring, which will 

 by and by become like to, and yet different from its parents. If we 

 mean by inheritance to include all that the living creature is or has 

 to start with in virtue of its genetic relation to its parents and 

 ancestors, then it is plain that the physical basis of inheritance is in 

 the fertilised ovum. As regards property, there is an obvious dis- 

 tinction between the inheritance and the person who inherits, but 

 there is no such distinction in biology. The fertilised egg-cell is the 

 inheritance, and is at the same time the potential inheritor. What 

 might be compared to an inheritance of property as apart from the 

 organism itself is the store of food which may be inside the egg, or 

 round about it. 



An organic inheritance means so much, even when we use the 

 magic word potentiality, that although we are quite sure that the 

 germ-cells constitute the physical basis of inheritance, we may con- 

 sider for a moment the difficulty which rises in the minds of many 

 when they remember that the egg-cell is often microscopic, and the 

 sperm-cell often only lu^V^oth OI> the ovum's size. Can there be 

 room, so to speak, in these minute elements for the complexity of 

 organisation supposed to be requisite? And the difficulty will be 

 increased if the current opinion be accepted that only the nuclei 

 within the germ-cells are the true bearers of the hereditary qualities. 

 Darwin spoke of the pinhead-like brain of the ant as the most 

 marvellous little piece of matter in the world, but must we not rank 

 as a greater marvel the microscopic germ-cells which contained 

 potentially all the inherited qualities of that ant, or of that man ? 



Nowhere more than in biology is one made to feel that a little 

 may go a long way. A microbic spore invisible even with a fairly 

 j^ood microscope may kill a man. From one microscopic egg of a 

 sea-urchin cut into three, Delage reared three larva?. In another 

 case he says that he reared an embryo from a J T th fraction of an egg. 



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