1892.] The Difficulties in the Heredity Theory. 541 
the body-cells and the germ-cells, as must exist if the Lamarck- 
ian theory is the true one. 
History of the Heredity Theory.—In a valuable summary 
of the past theories of heredity’ J. A. Thomson distinguishes 
three general problems, which are often confused. 1st. What 
characters distinguish the germ-cells from other cells of the 
body ? 2d. How do the germ-cells derive these distinguish- 
ing characters? 3d. How shall we interpret “ particulate ” 
inheritance, or the reappearance of single peculiarities in the 
offspring ? 
The various theories may be grouped under two heads, 
“ Pangenesis of Germ-cells” and “Continuity of Germ-cells,” 
according to the dominating idea in each. 
1. Pangenesis—The idea prevading pangenesis was first 
expressed by Democritus that the “seed” of animals was 
derived by contributions of material particles from all parts of 
the bodies of both sexes, and that like parts produced like. 
Two thousand years later, Buffon revived this conception of 
heredity in his “molecules organiques.” In 1864 Herbert 
Spencer suggested the existence of “physiological units,” derived 
from the body-cells of the parent, forming the germ+cells and 
‘then developing into the body-cells of the offspring. 
It is interesting to note the course of Darwin’s thought upon 
this matter in his published works and in his “Life and 
Letters.” He was at first strongly opposed to the views upon 
evolution advanced by Buffon, by Erasmus Darwin, his 
grandfather, expanded by Lamarck, and now known as 
Lamarckian. But gradually biddining convinced that his 
own theory of natural selection could not account for all the 
facts of evolution, he unconsciously became a strong advocate 
of Lamarck’s theory, and contributed to it a feature which 
Lamarck had entirely omitted, namely, a theory of heredity 
expressly designed to explain the transmission of wiquired 
characters. Darwin’s? “ provisional hypothesis of pangenesis ” 
postulated a material connection between the body-cells and 
1See Proc. Roy. Soc. Edin., 1888, p 
- See Animals and Plants under aiaiai, 1875, vol. ii., p. 349. - 
