308 BIOLOGY AND ITS MAKERS 



account for heredity, Darwin saw clearly the necessity 

 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 difficult 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 

 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 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 evenr 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 

 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 



,he 



