19 



There is a tendency to attribute every form of variation to 

 natural selection. To do so, it is necessary to expand the mean- 

 ing, so that natural selection becomes equivalent to selection by 

 nature, and thus the inseparable condition of a struggle for exis- 

 tence is ignored, without which struggle there can be no survival 

 of the fittest. There are of course variations which cannot be 

 accounted for by natural selection (survival of the fittest as 

 Herbert Spencer expresses it), such for example as the change in 

 the shape of the jaw in civilized races. 



A difficult point in the problem of heredity is the question 

 whether acquired variations are inherited. Part of the difficulty 

 is the definition of acquired variation. 



Weismann holds that acquired variations are never trans- 

 mitted, and there is certainly little or no trustworthy evidence of 

 mutilations being transmitted, while on the other hand numerous 

 experiments have failed to show that they can be transmitted. 

 Brown Esquard's experiments on guinea pigs stand alone in 

 favour of an occasional transmission, but serious doubts have 

 been thrown on the correctness of the interpretation he put on 

 the results obtained. 



Variation in unicellular forms and the lowest multicellular 

 beings is produced, in Weiemann's opinion, by the direct action 

 of the surrounding medium. Thus in amcBba the surrounding 

 medium has caused a differentiation of the cell protoplasm into 

 endo and ecto-sarc. In all forms having sexual reproduction 

 this fact is itself a cause of variation as no two individuals (at 

 least in higher animals) are exactly alike, and thus by heredity 

 the peculiarities of both parents are transmitted to the offspring, 

 which therefore differs from both parents. 



The Theory of Evolution does not confine itself to the ex- 

 planation of man's body alone, but may also be used to examine 

 into his mental and moral nature. This field has as yet been 

 but little investigated, and practically not at all by means of the 

 light thrown on it by NaegaH'sand Weismann's researches. These 

 researches will doubtless m the future produce valuable results 

 for the construction of true science of Sociology. 



WEDNESDAY, FEBRUARY 14th, 1894. 



THE MOVEMENT OF WATER IN TREES, 



BY 



MR. HENRY EDxMONDS, B.Sc. 



