74 A MIDLAND TILLAGE: GARDEN AND MEADOW. 



eat, or which the young themselves will most profit by when 

 they are fledged. The relation between the movements of 

 birds and their food is a problem which has not, so far as 

 I know, been fully investigated as yet ; but it is certain that 

 the minor migrations within a certain district are largely 

 due to two causes : (i) that already mentioned, the necessity 

 of proper food for the young both as nestlings and fledgelings ; 

 (2) the stress to which birds are driven by severe weather 

 and by the change of seasons. No one has as yet discovered any 

 one convincing reason for the great migrations of spring and 

 autumn, nor is it likely that there is one cause to be found 

 for them. But what influences birds in short journeys, influ- 

 ences them also, I have very little doubt, in long ones ; and 

 I believe that a more minute and scientific study of the food 

 of young and old during the breeding-time, and an exact 

 comparison of this with the food which supports them in the 

 winter, together with a final resolution of the much-debated 

 question whether they ever breed in their wint&r quarters, 

 would go far to throw some light upon the great mystery of 

 bird-life. Other problems of absorbing interest at present 

 occupy the attention of men of science. The sure foothold 

 which has been gained by the theory of development has 

 placed the great questions of classification in a new light, 

 and brought the struotwre of animals into the foreground ; the 

 microscope each year discovers new wonders in the development 

 of that structure from the earliest visible germ of life, and 

 the habits of the living animal, and the relations of animals 

 to each other, have consequently fallen a little into the back- 



