HEREDITY AND GERMINAL COXTIXUITY 3^7 



account for heredity, Darwin sa^^ clearly the necessity of 

 ]jroviding some mearis of getting all hereditar\- qualities com- 

 bined within the egg and the sperm. Accordingly he orig- 

 inated his pro\isional theory of pangenesis. Keeping in mind 

 the fact that all organism.s begin their lives in tlie condition 

 of single cells, the idea of inheritance through these micro- 

 scopic particles becomes difficult to understand. liow is it 

 possible to conceive of all the hereditary qualities being con- 

 tained within the microscopic germ of the future being? 

 Darv.'in 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 

 tissues, 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 gerniinal 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 reJ)resentati^'es of the tissues of the 

 parent form. 



Theory of Pangenesis Replaced by that of Germinal Con- 

 tinuity. — This theory of Darwin ser\-ed as the basis for other 

 theories founded upon the conception of the existence of |)an- 

 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 \arious 



