THE RETURN OF THE SWALLOW. 87 



Severn, down the Bristol Channel, and across the Irish Sea. 

 Further, it seems unreasonable to suppose that, granting the 

 ability, a swallow will move in one flight from such a climate as 

 that of Morocco to such an one as Ireland. And to put another 

 question: In the days of the immemorial coast line were tem- 

 perature and climatic circumstances just as they are at present, 

 and did the swallow require to migrate — if it was there at all to 

 do so ? Mr. Grant Allen also enunciates a theory of what he calls 

 " a sort of unconscious hereditary teaching by which the memory 

 of the lost land-connections has been handed down from one 

 generation of swallows to another since pre-glacial times." In these 

 times continuous land stretched from England to Africa, and, as 

 Mr. Allen says, the temperature of England was apparently as warm 

 as that of North Africa. Gradually both temperature and earth- 

 surface changed, and the swallow found it necessary to seek a 

 suitable climate, moving southwards in autumn and northwards in 

 spring, until the movement reached its present dimensions. The 

 English Channel and Mediterranean also came into existence, but 

 the migratory practice engrained in the system of the bird had 

 become a habit, and by this instinct these obstacles are over- 

 come. If it is true that a large body of swallows cross the 

 Mediterranean annually from Algeria to Marseilles, it is a most 

 noteworthy fact; but there is no great difficulty in seeing how the 

 passage can be accomplished by Malta and Italy, or Sardinia and 

 Corsica, or the Straits of Gibraltar. Gilbert White pointed out 

 the latter route, showing how little exposure there was incurred 

 by it and by the Straits of Dover. He says that his brother, who 

 lived in Andalusia, always found that some birds, and particularly 

 the swallow kind, are very sparing of their pains in crossing the 

 Mediterranean, taking the Tangiers and Gibraltar route quietly 

 and without any hurry. It is well known, too, that swallows 

 arriving on the Sussex coast take no rest, but go on their journey 

 northwards, as if quite fresh. My last question is : Why do 

 swallows migrate northwards, leaving the clear sunny atmosphere 

 of the shores of the Mediterranean and seeking the grey skies of 

 Northern Europe? As far north as Lapland, Siberia, Nova 

 Zembla, and Iceland, they go. They must perish in thousands 

 upon thousands as they move; and it may well be asked what 

 advantage is it to them to spend the summer in northern latitudes ? 



