THE RETURN OF THE SWALLOWS. 15 



force ; and they leave us again in August, while the 

 swallows linger on till the late autumn. Both kinds fly 

 low and open-mouthed over the most flowery meadows, 

 where they catch honey-sucking insects in abundance ; 

 or over the ponds and rivers, where they meet with in- 

 numerable mayflies and* other winged species, whose 

 larvae live as caddis-worms or the like under water, while 

 the perfect insects hover above it to lay their eggs upon 

 the surface. 



The question as to the supposed instinctive feelings 

 which drive the swallows north or south at the proper 

 season is an extremely interesting one ; and perhaps only 

 very recent views as to the nature of climatic changes 

 and zones can enable us in time to give the true explana- 

 tion. Hitherto it has been usual to think of the differ- 

 ences of climate between Europe and Africa as though 

 they had always been permanent, and so to raise unneces- 

 sary difficulties in the way of a rational solution to the 

 problem. If England had always had a cold winter, 

 while Algeria always had a warm one, and if a double 

 belt of sea had always separated us from the two conti- 

 nents, it would indeed be hard to understand how an 

 English bird could first bethink itself of moving south- 

 ward in winter, or how an Algerian bird could ever be 

 seized with an original impulse to go northward in the 

 spring-time. It is not surprising, therefore, that early 

 naturalists should have taken refuge in the hypothesis of 

 a special instinct implanted in the swallows, independ- 

 ently of experience, and prompting them to seek the ap- 

 propriate climate by some unknown " sense of direction" 

 at the proper times of year. But, with our existing 

 knowledge as to the past history of European geography 

 and meteorology, no such cutting of the Gordian knot is 

 now necessary. 



