116 



No one appears to have called attention to the fact that 

 "whereas the hereditary desire to leave the breeding grounds in the 

 autumn appears to act with the greatest force in the case of the 

 young of the year, the desire to again 'return thither appears on 

 the contrary to be greatest in the oldest and most vigorous males. 

 If this assumption is correct we may reasonably suppose that the 

 hereditary impulse to leave the breeding grounds loses strength 

 as the individual grows older, whilst the desire to return thither 

 at the earliest possible date, on the other hand seems to gain 

 additional force. These considerations may even point to the 

 fact that it was the young which first set out on those daily 

 journeys in search of food before described, and may shed some 

 light on the theory that they feel the influence of the hereditary 

 desire to migrate earlier in the autumn than do their parents. 



Herr Gatke points out that those migratory flights occurring 

 late in November and December are composed exclusively of fine 

 adult males of various species. No doubt, unless compelled by 

 the advent of exceptional cold, these old and robust individuals 

 would have remained on the outskirts of the frost until the 

 following spring. At the same time it must not be forgotten that 

 at one period winter in the north most probably set in much 

 earlier than it does at the present time. 



It has already been pointed out that birds are possessed of 

 a very highly developed sense of locality or direction. It remains 

 to be shown how young birds, with the aid of this power, are 

 enabled without previous experience to migrate to winter quar- 

 ters which they have never before seen. The desire to migrate 

 is due, as has already been stated, to hereditary impulse to 

 leave the breeding grounds. The manner in which this 

 impulse has been acquired has also been described. To the 

 writer there is no difficulty in assuming that the possession of 

 the sense of locality and direction is also due to heredity. This 

 view gains additional force from the fact that this power of 

 orientation varies both in individuals and tribes, not only with 

 man but also and in the same degree with birds, both as regards 

 individuals and species. Amongst the latter it is those species 

 which are the most migratory who possess the sense in its highest 

 development, whilst those on the other hand who perform no 



