119 



Enough has now been written on the varying degree of 

 strength in which the migrating instinct is present in local races 

 and species of birds. It may be here remarked that the term 

 hereditary instinct or hereditary impulse, has been objected to on 

 the grounds that it is merely a method of evading a dif&culty or 

 expressing our ignorance of the means by which an animal or 

 bird is impelled to perform, or accomplishes certain actions. 

 Such terms, however, are a necessity, and the objection loses its 

 force when the instinct or impulse can be proved to exist with 

 different species in greatly varying degree. We can never expect 

 to understand the actual mechanism or process set in motion in 

 the brain, either in following out a thought or performing an 

 unconscious act. Possibly if we could communicate our difficulty 

 to a bird we might get a similar reply to that which Von Midden- 

 dorf — who first promulgated the theory of a " sense of direction," 

 — received from the Samoyede, whom he questioned on this 

 point. "Well," answered the latter, after regarding him with 

 surprise, " how is it that the little arctic fox finds her way on the 

 great Tundra without ever going astray ? " This Samoyede, 

 though conscious of his own powers, was quite as much at a loss 

 to account for their possession or how they acted, as we ourselves 

 would be if called upon to explain the various mental processes 

 taking place in our own brains. 



Beyond the bare statement that such is not the case, Herr 

 Gatke produces but little evidence in opposition to the theory that 

 migration is conducted at lower elevations during the hours of 

 darkness than is the case during bright clear daylight. Evidence 

 collected at lighthouses and hght-ships, however, seems to point to 

 the truth of this assertion. In view of this fact it may be remarked 

 that there is some evidence in favour of the theory that sight 

 comes in as an additional aid to the sense by means of which 

 birds are enabled to find their way. We can hardly imagine a 

 " sense of direction or locality " to be so acute as to enable any 

 bird like a Wagtail or Flycatcher to set out from its winter 

 quarters and accomplish the whole journey without a halt, to 

 some familiar field or garden, containing the cowshed, or summer- 

 house, on the door-hinge of which it had been in the habit of con- 

 structing its nest. Of course in the case of young birds there can 



