220 LEISURE-TIME STUDIES. 



and foot. Salvator's family likewise consisted of four 

 children, three of whom possessed the six fingers and six 

 toes of their father and grandparent; the fourth and 

 youngest possessing the ordinary number of digits. The 

 four mothers of the second generation of Kelleias ex- 

 hibited no abnormality in respect of hands or feet, and 

 hence the hereditary influence of the female parent doubt- 

 less made itself felt in the development of a proportion of 

 normal hands and feet, although, as far as the genealogy 

 of the family is traced, the proportion of six-fingered and 

 six-toed members clearly tends to exceed that of those pos- 

 sessing the nomal number of fingers and toes. 



Having thus selected and marshalled some of the chief 

 facts relating to the occurrence of heredity or the likeness 

 between parent and offspring, it may be fairly urged that 

 these facts seem to establish the existence of some well- 

 defined law, in virtue of which the bodily structure, the 

 mental characteristics, or even the peculiarities induced by 

 disease, are transmitted from one generation to another. 

 And it also becomes an important study to determine the 

 causes which operate in producing such variations in the law 

 of inheritance as we have endeavoured to illustrate in the 

 case of certain groups of lower animals. Can we, in other 

 words, account for the similarities and resemblances, and 

 for the diversities and variations, which living beings present, 

 apparently as a natural sequence of their life, and of the 

 operation of the laws which regulate that existence ? The 

 answer to some such question as the preceding closely 

 engaged the attention of physiologists in former years, the 

 result of their considerations being the framing of various 

 theories whereby the facts of heredity could be correlated 

 and explained. It is evident that any explanation of 

 heredity must partake of the nature of a mere speculation, 

 from our sheer inability to penetrate deeper into the in- 

 vestigation of its laws than the observation of phenomena 

 can lead us. But when rightly employed, generalisations 

 and theories serve as leading-strings to the truth ; and, 



