CHAPTER III 



THE GERM-CELLS 

 I.— HISTORICAL. 



Nothing will be more helpful towards a right appreciation 

 of the fundamental facts of our subject than a proper 

 understanding of their historical relationship. One is apt 

 to become impatient when lost in a tangle of dark and un- 

 known paths, leading, it seems, nowhither — and the science 

 of Heredity often leaves us in such a maze ; but it would 

 be wise to take into consideration, not what has still to be 

 achieved, which is much, but what has already been 

 attained, which is not little. We shall find that nearly 

 our whole knowledge of the subject is of very recent date 

 indeed, and shall therefore be less surprised to find that 

 so many problems of this most important branch of human 

 inquiry are still unsolved. 



For one who is accustomed to look upon biology from the 

 modern point of view, it is nearly an impossibility to revert 

 to the state prevalent at the time when the cell as the unit 

 of the organism was unknown. And yet it was only in 

 1838 that Schleiden for the first time demonstrated the 

 cell-structure of plants, showing that plants were not only 

 built up of cells, but also took their origin from a single cell, 

 the ovum. The same was proved by Schwann in the 

 following year, 1839, to apply to the animal kingdom. Up 

 to then cells had occasionally been seen with the micro- 

 scope, but, as the name implies, they had been looked upon 

 as " cells " — i.e., cavities filled with air. Only gradually 

 were they recognized to be solid bodies having contents, 



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