SCOPE OF GENETICS 21 



breed, eai*s of intermediate length are pro- 

 duced : and that these intermediates breed 

 approximately true. 



Exceptions in general must be discussed 

 elsewhere. Nevertheless if I may throw out 

 a word of counsel to beginners, it is : Treasure 

 your exceptions! When there are none, 

 the work gets so dull that no one cares to 

 carry it further. Keep them always un- 

 covered and in sight. Exceptions are like 

 the rough brickwork of a growing building 

 which tells that there is more to come and 

 shows where the next construction is to be. _ 



You will readily understand that the 

 presentation here given of the phenomena 

 is only the barest possible outline. Some of 

 the details we may now fill in. For example, 

 I have spoken of the characters of the 

 organism, its colour, shape, and the like, as if 

 they were due each to one ingredient or factor. 

 Some of them are no doubt correctly so 



