THE WONDERS OF LIFE 



features in the plasm of the germ-cells; because it is 

 this germ-plasm of the maternal ovum and the paternal 

 sperm - cell that conveys the characteristics of the 

 parents to the child. Hence the great progress that has 

 been made recently in the study of conception and 

 heredity, by means of a number of remarkable observa- 

 tions and experiments, has been of service to our ideas 

 on the molecular structure of the plasm. I have dealt 

 with the chief of these theories in the ninth chapter of 

 my History of Creation y and must refer the reader thereto. 

 In chronological order we have: (i) the pangenesis 

 theory of Darwin (1868), (2) the perigenesis theory of 

 Haeckel(i875), (3) the idioplasm theory of NageH (1884), 

 (4) the germ -plasm theory of Weismann (1885), and (5) 

 the mutation-theory of De Bries (1889). None of these 

 attempts, and none of the later theories of heredity, has 

 given us a satisfactory and generally admitted idea of 

 the plasma-structure. We are not even clear as to 

 whether in the last resort life is to be traced to the 

 several molecules, or to groups of molecules, in the 

 plasm. With an eye to this latter difference, we may 

 distinguish the plastidule and micellar theories as two 

 different groups of relevant hypotheses. 



In my essay on "The Perigenesis of the Plastidules" 

 (1875) I formulated the hypothesis that in the last 

 instance the plastidules are the vehicles of heredity — 

 that is to say, plasma-molecules which have the property 

 of memory. In this I found support in the ingenious 

 theory of the distinguished physiologist, Ewald Hering, 

 who had declared in 1870 that "memory is a general 

 property of organic matter." I do not see still how 

 heredity can be explained without this assumption ! The 

 very word "reproduction," which is common to both 

 processes, expresses the common character of psychic 

 memory (as a function of the brain). By plastidules I 

 understand simple molecules; the homogeneous nature 



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