THE CELLULAR BASIS 111 



phenomena of inheritance have been dis- 

 covered in the absence of any definite knowl- 

 edge of the mechanism of heredity, a scientific 

 explanation of these phenomena must wait 

 upon the knowledge of their causes. In the 

 absence of such knowledge it has been neces- 

 sary to formulate theories of heredity to ac- 

 count for the facts, but these theories are only 

 temporary scaffolding to bridge the gaps in 

 our knowledge, and if we knew all that could 

 be known about the germ cells and their de- 

 velopment we should have little need for 

 theories. In the first lecture we looked at the 

 germ cells and their development from the 

 outside, as it were ; let us now look inside these 

 cells and study their minuter structures and 

 functions. 



Only a beginning has been made in this 

 minute study of the germ cells and of their 

 transformation into the developed animal, 

 and it seems probable that it may engage the 

 attention of many future generations of bi- 

 ologists, but nevertheless we have come far 

 since that day, only about thirty-five years 

 ago, when Oscar Hertwig first saw the ap- 



