38 LEPIDOPTEKA. 



dition, others even at a very early date were in a dilapidated 

 state. — 4. Most of the captures were of the Scandinavian 

 type, that is, were of a finer texture than continental ex- 

 amples, and were adorned with the white border. 



On the other hand, it has been argued that if the butter- 

 flies had travelled three or four hundred miles over the sea, 

 they could not possibly have been in such fine condition as 

 most of them undoubtedly were ; that if a migration had 

 taken place, a large body of them would have arrived toge- 

 ther at one spot, and that their appearance simultaneously on 

 the east and south coasts militates against the probability that 

 they had migrated from Norway. 



To me the greatest obstacle seems the rapidity and dura- 

 tion of their flight, for from Norway to the nearest Scotch 

 point represents a distance of, say, three hundred miles; and 

 to accomplish this, they would have to fly continuously for 

 twelve hours, at the rate of about a mile in less than two and- 

 a-half minutes, and butterflies usually face the wind. But 

 if they landed at Norfolk, the distance would be about four 

 hundred miles; and if their transit occupied six hours, their 

 velocity would equal that of an express train. 



Now, amongst the recorded captures are some, we cannot 

 say how many, yellow-bordered specimens; and Mr. Stainton 

 informs us that both forms occur in Holland, a country 

 situated about one hundred miles from the coast of Norfolk 

 and Suflfolk, giving over three and-a-half minutes per mile for 

 a six hours' journey. 



It seems to me that the migratory hypothesis is the only 

 one which can hold water, for it is inconceivable that the 

 earlier stages of the insect, supposing it to have bred in the 

 country, should have been so entirely overlooked; and again, 

 if our visitors had been true British born, it is only natural 

 to suppose that their appearance in the North would have 



