Phenomena of Inheritance 67 



weighs only 175 milligrams, or about one three-millionth part of 

 the body weight, and in hereditary cataract only about one twen- 

 tieth part of the lens becomes opaque, and yet this minute frac- 

 tion of the body weight shows the influence of heredity. Even 

 the size, shape and number of the cells in certain organs, and in 

 given embryonic stages, may be repeated generation after gener- 

 ation; and if our analysis were sufficiently complete we should 

 doubtless find that even the minute parts of cells, such as nuclei, 

 chromosomes and centrosomes, show individual peculiarities which 

 are inherited. 



(b) Physiological peculiarities are inherited as well as morpho- 



105 



43 



FIG. 22. DIAGRAM OF EIGHT DIFFERENT RACES OF Paramedum, each hori- 

 zontal row (A-H) representing a single race. The individual showing the 

 mean size in each race is indicated by -\- ; the mean of all the races is shown 

 by the line X-X. The numbers are the lengths in micra (thousandths of 

 a millimeter), X 43- (After Jennings.) 



