HEREDITARY CHARACTERS 



AND THEIR MODES OF TRANSMISSION 

 CHAPTER I 



The structure of living matter Unicellular and multicellular animals and 

 plants Life cycles of unicellular animals Reproduction in multicellular 

 animals and plants The life cycles of multicellular organisms Theories of 

 emboitement, pangenesis, and idioplasm Experiments bearing upon these 

 theories. 



THE phenomenon of heredity, or the transmission of char- 

 acters from parents to offspring, is exhibited by all living 

 organisms, both animals and plants. But before dealing 

 with heredity directly, it is necessary to examine some other 

 properties which are also common to all living organisms. 



As far as our knowledge goes, living matter, whether it 

 be animal or vegetable, exists in only one form, that is, as 

 minute masses of a complex jelly-like substance known 

 as protoplasm. The minute masses are called cells, and 

 are composed of certain definite parts. Cells when not 

 pressed upon by surrounding cells or specially modified, 

 are roughly spherical in shape. Within each cell is an area, 

 generally surrounded by a membrane, which is denser than 

 and differs in some other ways from the rest of the cell. 

 This is the nucleus. The rest of the protoplasm forming 

 the cell is known as the cytoplasm. There are other organs 

 usually found in cells, but for the present we shall confine 

 ourselves to the nucleus and cytoplasm. 



Every part that is alive of an animal or plant consists of 

 cells and of nothing else. There are parts of the bodies 

 of animals and plants that are not composed of cells, but 

 these are not alive. The hard parts of the bones in man 



