NON-MATHEMATICAL SCIENCES 187 



covery of Mendel's law and the study of chro- 

 mosomes have given an impetus comparable to 

 that given to mechanics by the discoveries of 

 Galileo and Newton. 



It seems that every individual organism, as 

 well as every typical cell, has a dual nature. As 

 the animals entered the ark two by two, so the 

 various factors of heredity enter the cell in 

 pairs. On the other hand, the special cells of 

 reproduction result from a process of bisection, 

 so that each possesses but one member of every 

 pair. When such paternal and maternal cells 

 unite, the new individual once more possesses the 

 complete quota of pairs, but it has only half of 

 the heredity factors of the father and only half 

 of those of the mother. It appears to be an abso- 

 lutely level chance which half of any one pater- 

 nal or maternal pair enters into the offspring. 

 This is a rough statement of the famous law of 

 Mendel, which reduces the whole science of 

 genetics to a simple problem in the theory of 

 probability. 



As so often happens in science, this law of 

 Mendel was almost forgotten until a mechanism 

 was discovered whereby it could be interpreted. 

 The modern investigations of chromosomes 

 have brought into biology a degree of unity 



