88 



HEREDITY. 



^ f 



A Simple 

 Explanation of 

 Reproduction. 



Weismann's 

 Theory. 



Chromatin. 



parent life, having in its organism, in rudiment- 

 ary form, all the attributes of its parent. The 

 anatomy of this rudimentary psychic organism is 

 what we call a germ-cell, and it forms the physical 

 basis of the new life. As the rudimentary organ- 

 ism develops it becomes more and more complex 

 both in its anatomy and its psychic nature, until 

 it is finally a duplicate, a reproduction, anatomic- 

 ally, physiologically and psychologically of its 

 parent. 



To simplify : suppose we have a simple organ- 

 ism composed of five psychic units (cells). Each 

 of these five units is in reality, as we have seen, 

 an organism having the power to reproduce itself ; 

 but in the larger or five-celled organism, each 

 unit has its specific function to perform. As in 

 the single-celled organism a nucleus is formed 

 and cast off as a means of reproduction, so in the 

 five-celled organism each of the five units will give 



Galton must be given much of the credit of clearly stating 

 it as a fact. Similar views have been more recently popu- 

 larized among biologists by the voluminous writings of 

 Weismann on "the continuity of the germ-plasm." 



In 1883 Weismann began to advance a theory of heredity 

 differing in many particulars from all its predecessors. It is 

 based upon the facts recently discovered regarding the struc- 

 ture and physiology of the cell. It has been productive of 

 more discussion and comment than any biological specula- 

 tion since the appearance of Darwin's "Origin of Species." 

 Weismann holds that inheritance in the many celled animals 

 metazoa and multicellular plants takes place through the 

 germ-cells, the egg and spermatozoon in animals, and cor- 

 responding cells, known under various names, in plants. 

 Since the offspring may inherit from either parent, the 

 means for the transmission of ancestral traits must be the 

 same in both the male and female products. By carefully 



