HEREDITY AND GERMINAL CONTINUITY = 3°7 
account for heredity, Darwin saw clearly the necessity of 
providing some means of getting all hereditary qualities com- 
bined within the egg and the sperm. Accordingly he orig- 
inated his provisional theory of pangenesis. Keeping in mind 
the fact that all organisms begin their lives in the condition 
of single cells, the idea of inheritance through these micro- 
scopic particles becomes difhcult to understand. How is it 
possible to conceive of all the hereditary qualities being con- 
tained within the microscopic germ of the future being? 
Darwin supposed that very minute particles, which he called 
gemmules, were set free from all the cells in the body, those 
of the muscular system, of the nervous system, of the bony 
tissucs, and of all other tissues contributing their part. These 
liberated gemmules were supposed to be carried by the cir- 
culation and ultimately to be aggregated within the germinal 
elements (ovum and sperm). Thus the germinal elements 
would be a composite of substances derived from all organs 
and all tissues. 
With this conception of the blending of the parental 
qualities within the germinal elements we can conceive how 
inheritance would be possible and how there might be in- 
cluded in the egg and the sperm a representative in material 
substance of all the qualities of the parents. Since develop- 
ment begins in a fertilized ovum, this complex would contain 
minute particles derived from every part of the bodies of 
both parents, which by growth would give rise to new tissues, 
all of them containing representatives of the tissues of the 
parent form. 
Theory of Pangenesis Replaced by that of Germinal Con- 
tinuity.—This theory of Darwin served as the basis for other 
theories founded upon the conception of the existence of pan- 
gens; and although the modifications of Spencer, Brooks, and 
others were important, it is not necessary to indicate them in 
detail in order to understand what is to follow. The various 
