Heredity and the Origin of Variations. 123 



constitution, in so extraordinary a manner, apparently 

 proves that the state of the parents at the exact period of 

 conception, or the nature of the subsequent embryonic 

 development, has a direct and powerful influence on the 

 character of the offspring." But a little consideration will 

 show that, though this might, in the absence of a better 

 explanation, account for variation in character, it could not 

 account for variation in form and feature, unless we regard 

 these as in some way determined by the character. More- 

 over, as we shall see presently, it is open to question 

 whether acquired modifications of structure or character in 

 the parent can in any way influence the offspring. Again, 

 in the litter of puppies born of the same bitch by the same 

 dog there are individual variations, often as well marked 

 as those in successive births. 



The facts, then, to be accounted for are — first, the close 

 hereditary resemblance in all essential points of offspring 

 to parent ; and, secondly, the individual differences in 

 minor points among the offspring produced simultaneously 

 or successively by the same parents. These are the facts 

 as they occur in the higher animals. It will be well to 

 lead up to our consideration of them by a preliminary 

 survey of the facts as they are exemplified by some of the 

 lower organisms. 



In the simpler protozoa, where fission occurs, and where 

 the organism is composed of a single cell, where also there 

 is a single nucleus which apparently undergoes division 

 into two equal and similar parts, it is easy to understand 

 that the two organisms thus resulting from the halving of 

 a single organism partake completely of its nature. If the 

 fission of an amoeba is such as to divide it into two similar 

 parts, there is no reason why these two similar parts 

 should not be in all respects alike, and should not, by the 

 assimilation of new material, acquire the size and all the 

 characteristics of the parent form. In the higher and 

 more differentiated protozoa, the case is not quite so simple; 

 for the two halves are not each like the whole parent, but 

 have to be remodelled into a similar organism. But if we 



