THE MODES OF REPRODUCTION 19 



of an inch in diameter, yet her daughter may display 

 the very tones of her mother's voice, her very ges- 

 tures, even her most intimate mental peculiarities. 

 Plainly we have now come upon a problem indeed ! 



It is our business, then, to examine, with the utmost 

 particularity which the microscope and the modern 

 methods of staining organic tissues permit, the 

 characters of the minute but immeasurably poten- 

 tial cells by which the higher animals and plants 

 reproduce themselves. We shall find, as might be 

 expected, that they tend to be typical of cells in 

 general — not highly dift'ercntiated. A bone cell, a 

 nerve cell, a liver cell, a muscle cell, diflfer widely 

 from the typical cell form ; but the cell which is 

 destined to give rise to all these forms, and a 

 thousand more, is comprehensively typical of all 

 other kinds of cells, but of none in especial. 



Let us, then, consider a typical animal ovum — not 

 of any species in particular. It is a minute globular 

 body, usually invisible to the naked eye, and is 

 bounded by a thin cell-membrane. The body of 

 the cell consists of a granular, semi-solid substance, 

 which is alive, and which is an example of proto- 

 plasm — the "physical basis of life." Somewhere 

 about the centre of the cell there is a minute, rather 

 denser speck, which we call the nucleus. Stained 

 with appropriate dyes this nucleus displays a net- 

 work of linely interlacing fibres. This network takes 

 the dye colour deeply, and is therefore known as the 

 chromatin of the nucleus. Weismann has taught 

 us to regard it as the bearer of hereditary characters. 

 Just beside the nucleus — in the large majority of 

 cases — is a nmch smaller speck which is called the 



