HEREDITY AND EVOLUTION 101 



main secret of subsequent development. There 

 seems much that is helpful in the suggestion which 

 Weismann tells us operated on his mind in the 

 course of his researches. He says : The facts of 

 the transmission of hereditary tendencies from both 

 parents to the child, together with the fact of 

 parthenogenesis, 1 induced me at an early date to 

 look for the essence of fertilisation, neither in the 

 vitalisation of the egg, nor in the union of two 

 opposed polar forces, but rather in the fusion of two 

 hereditary tendencies. 2 This last seems to state 

 exactly what the facts require. At the same time, 

 the aid here found towards explanation of procedure 

 of germ-cells, is obtained at the cost of the hypothesis 

 of isolation of germ-plasm from the action of the 

 parent body. The fusion of two hereditary tendencies 

 affords, under the laws of heredity, support for 

 progressiveness in organic life ; but transmission of 

 hereditary tendencies from both parents to the child, 

 implies something more than transmission of the 

 common characteristics of the species, and thus 

 requires modification of the hypothesis. This demand 

 is further strengthened by what is known of the 

 dependence of offspring on parental vigour, and the 

 evil consequences to progeny of diminished health 

 in either parent, as well as by the mass of evidence 

 affecting the lower animals, accumulated by Darwin, 

 Wallace, and other naturalists. 



Passing now from the sphere of microscopic 

 research, we next take a more general view of the 

 phenomena of heredity, as concerned with organic 



1 P. 91. 



2 



Jc. yi. 



Essays on Heredity, 2nd edition, vol. ii. p. 111. 



