INTRODUCTiON 9 



not referring to it in my essays which appeared nearly ten years 

 later.* In one of these essays 'On Heredity' (1883), I con- 

 tested at first in general terms not only the existence but also 

 the theoretical possibility of the transmission of acquired charac- 

 ters, and tried to release the theory from the necessity of an 

 explanation which deprived it of any further development. In 

 this essay I further assumed the existence in the germ-cell of a 

 reproductive substance, the germ-plasm^ which cannot be formed 

 spontaneously, but is always passed on from the germ-cell in 

 which an organism originates in direct coiititmity to the germ- 

 cells of the succeeding generations. The diiTerence between the 

 • boay ' in the narrower sense (soma) and the reproductive cells 

 was also emphasised, and it was maintained that the germ-cells 

 alone transmit the reproductive substance or germ-plasm in unin- 

 terrupted succession from one generation to the next, while the 

 body (soma) which bears and nourishes the germ-cells, is, in a 

 certain sense, onlv an outgrowth from one of them. 



A second attempt to improve upon the theory of pangenesis 

 must be considered here. I have already referred elsewhere f to 

 the interesting and ingenious book on ' The Laws of Heredity,' % 

 by W. K. Brooks. The author retains the fundamental points 

 of this theory, viz., the formation of gemmules in all the cells 

 of the body, their circulation through the latter, and their aggre- 

 gation in the germ-cells or buds : he dilTers, however, from 

 Darwin principally in ascribing to the male germ-cell a particu- 

 larly strong power of attraction for the gemmules, so that it 

 collects a special mass of them and stores them up. As this 

 assumption is made chiefly for the purpose of explaining varia- 



* These essays first appeared separately in the years 1881-91. The only 

 complete edition of the collected essays which has hitherto appeared is the 

 English translation, ' Essays upon Heredity and Kindred Biological Prob- 

 lems ' (edited by Poulton, Schonland, and Shipley, Oxford, 1889), contain- 

 ing Essays I, — VIII. A second edition appeared in 1891 as Vol. I., and 

 Essays IX. — XII. follow this year as \'ol. II. A French translation of all 

 these essays, with the exception of the last on ' Amphimixis,' cS:c., has also 

 appeared with the title, ' Essais siir I'Heredite et la Selection Xaturelle,' 

 traduits par Henry de Varigny, Paris, 1892. 



t ' The Significance of Sexual Reproduction in the Theory of Natural 

 Selection.' — ' Essays upon Heredity,' p. 326. 



t W. K. Brooks, ' The Laws of Heredity, a Study of the Cause of 

 Variation and the Origin of Living Organisms,' Baltimore, 1883. 



