METHOD OF STARTING INVESTIGATIONS. 53 



investigation, was to reach as quickly as pos- 

 sible a crucial test or a crucial observation 

 that would enable him to determine positively 

 whether or not his beliefs were justified. As 

 soon as the idea of descent of species took 

 definite shape in his mind, he determined, 

 after deliberation, to take up the study of 

 domestic pigeons. 1 He selected these because 

 the variations were more numerous and plainer, 

 more of them had arisen in the historical period 

 than is usual with animal groups, the material 

 was abundant and easily accessible, etc. He 

 cnose for his investigation the conditions most 

 favorable to success. 



When he discovered that insects are caught 

 in large numbers by the common sundew, he 

 gathered a number of plants, counted the leaves 

 and the number that had caught insects ; and 

 compared the results with the accidental de- 

 struction of insects by the viscous buds of the 

 horse-chestnut, etc. 2 Similar results were pro- 

 duced by somewhat similar means; but by the 

 comparison he secured preliminary evidence 

 that the leaves of the sundew, unlike the buds 

 of the horse-chestnut, were excellently adapted 



1 Origin of Species, p. 15; Variation of Animals and 

 Plants under Domestication, Vol. I. p. 137. 



2 Insectivorous Plants, pp. 1-3, 63-76. 



