UNSOLVED PROBLEMS. 149 



land and sea. Here we have, in the first place, instead of 

 individual animals, large bodies or flocks traversing great 

 distances. It may be that all members of the flock have 

 previously traversed the same ground or distance, or at 

 least that many of them have done so, and that there are 

 leaders, specially intelligent, observant, and experienced, 

 who are implicitly followed by the others ; but it is difficult 

 or impossible to understand what means the birds can have 

 at sea of judging of locality, or how they can recognise land- 



ks across the whole continent of Europe and the whole 

 length of the British Islands. No proper explanation is 

 offered as to the sort of guidance the birds have in crossing 

 long stretches of sea or land by night. 



According to Eae, Mackay, and other travellers in Arctic 

 America, such animals as the reindeer and buffalo, at certain 

 seasons or under certain conditions, travel due south or north, 

 as the case may be, the procedure being invariable in given 

 circumstances in the same species. In such a case there is 

 no evidence that any special locality is sought for, nor does 

 it appear how far north or south the animal herds wander, 

 for their travel is more like an indefinite wandering than a 

 specific way-finding. But it is asserted that the animals at 

 least maintain a course that is northerly or southerly, or 

 due north or south, while it is suggested that they do so by 

 reason of a sense of polarity. 



Immense migrations of butterflies occur annually in 

 Central and South America, always from and in the same 

 direction, there being no return swarms (Belt). The same 

 occurs in the Norwegian lemming, in which, however, the 

 point ultimately reached by the mass of emigrants is usually, 

 if not always, deteriniuable. In their case it is the sea, into 

 which they rush headlong and perish wholesale by drowning. 

 Their migrations have, moreover, frequently been observed 

 at various of their stages. They are characterised inter alia 

 by the following singular phenomena : The animals march 

 in armies, in straight lines unswervingly, climbing labori- 

 ously up and over physical obstacles instead of simply avoid- 

 ing them, exhibiting a morbid pertinacity or determination 

 in adhering to their own mode of way-making, committing 



