Heredity. 141 



continually occur, in other words, as resemblance is often 

 incomplete , the formula has to be altered to " Like tends 

 to beget like". (2) Besides the gene^i! resemblance, 

 which expresses the relative constancy of the species, a 

 particular similarity is often demonstrable. The off- 

 spring reproduces not only the general features, but 

 often minute characteristics of its parents, or of one of 

 them, and this applies to abnormal as well as to normal 

 characters. (3) In many instances the offspring ex- 

 hibits, not only parental, but also grandparental char- 

 acteristics; the inheritance of an organism may be 

 compared to a mosaic built up from many ancestors. 

 As Galton has shown, each parent contributes on an 

 average to the heritage of the offspring one-fourth, 

 each grandparent one-sixteenth, and so on. (4) The 

 fact in regard to the explanation of which most de- 

 bate at present obtains, is that characters individually 

 acquired by the parent as the results of environmental 

 or of functional influence, may reappear in the offspring. 

 (5) Throughout successive generations there is, Galton 

 maintains, a tendency to sustain the specific type or 

 average, by the continued approximation of the progeny 

 of exceptional forms towards the mean of the species. 



There are at present three main problems of heredity, 

 which must be carefully distinguished, as Problems of 

 has not always been done. Heredity. 



1. What accounts for the unique character of the 



germ-cells? 



2. Granted the unique character of the germ, what 



are the conditions of its reconstructing a form 

 like the parent? 



3. What are the facts in regard to the reappear- 



ance of individual peculiarities or modifications, 

 acquired by the parent as the result of changes 

 in function or environment? Are they trans- 

 missible? 



(a) Early Hypotheses. We need not, however, discuss 

 the possession of the germs by spirits, nor yet the pos- 

 tulates of vires formativce, nisus formativus, principle of 

 heredity, Vererbungskraft, or Bildungstrieb, but begin 



