304 THE HISTORY AND SCOPE OF ZOOLOGY IX 



physiology pursued by medical men, nor again was it 

 included in the field of microscopy and the cell-theory. 

 The area of biological knowledge which Darwin, was 

 the first to subject to scientific method and to render, 

 as it were, contributory to the great stream formed 

 by the union of the various branches, the outlines of 

 which we have already traced, is that which relates to 

 the breeding of animals and plants, their congenital 

 variations, and the transmission and perpetuation of 

 those variations. This branch of biological science 

 may be called Thremmatology (Ope^a, " a thing 

 bred"). Outside the scientific world an immense 

 mass of observation and experiment had grown up in 

 relation to this subject. From the earliest times the 

 shepherd, the farmer, the horticulturist, and the 

 " fancier " had for practical purposes made themselves 

 acquainted with a number of biological laws, and 

 successfully applied them without exciting more than 

 an occasional notice from the academic students of 

 Biology. It is one of Darwin's great merits to have 

 made use of these observations and to have formu- 

 lated their results to a large extent as the laws of 

 variation and heredity. As the breeder selects a con- 

 genital variation which suits his requirements, and by 

 breeding from the animals (or plants) exhibiting that 

 variation obtains a new breed specially characterised 

 by that variation, so in nature is there a selection 

 amongst all the congenital variations of each genera- 

 tion of a species. This selection depends on the fact 

 that more young are born than the natural provision 

 of food will support. In consequence of this excess 



