Earlier Theories of Heredity 5 



book entitled Animals and plants under domestication 

 and was called pangenesis. In a certain sense DARWIN 

 apologized for pangenesis, realizing that knowledge had 

 not advanced far enough for the construction of any 

 adequate theory. The theory of pangenesis, therefore, 

 is to be regarded more as a suggestion than as a formula- 

 tion of belief. 



The theory may be summarized as involving two 

 theses which should be kept distinct. The first thesis, 

 in DARWIN'S words, is as follows: "The individual 

 cells and organs of the whole organism are represented in 

 every germ cell and bud by definite material particles. 

 These multiply by division, and at cell division pass on 

 from the mother cells to the daughter cells." This is the 

 essential feature of pangenesis; that is, every germ cell 

 (egg or sperm) contains dividing particles that in cell 

 division pass on to every cell produced. This statement 

 agrees in general with the facts recognized today under 

 a somewhat different terminology, it being only neces- 

 sary to call these particles chromosomes. This is re- 

 markable when it is remembered that the statement was 

 made fifty years ago. 



"The second thesis is as follows: "All the cells of the 

 body throw off particles at various periods of their 

 development. These reach the germ cells and hand 

 over to them any characters of the organism which they 

 may lack." This is known as the transportation hy- 

 pothesis and was an attempt to account for certain facts 

 which seemed to indicate the inheritance of acquired 

 characters. It is somewhat surprising to find DARWIN 

 explaining heredity on the basis of the inheritance of 

 acquired characters, for his theory of the origin of 



