8 VESPERTILIONID^. 



as their prey performs its various gyrations to escape 

 from them. These easy and graceful evolutions present 

 an interesting scene, in perfect harmony with the quiet 

 of a calm summer evening, and possessed of sufficient 

 animation to relieve the sameness and gloom of the hour, 

 without interrupting its stillness and tranquillity. 



Do our Bats ever migrate ? or do Swallows ever hiber- 

 nate ? To these questions, unhesitatingly answered in 

 the negative in the first edition of this work, we pro- 

 bably have still to make the same reply. But by 

 extending the inquiry to the European species, we shall 

 probably have to give a qualified affirmative to the first 

 of them. It has been ascertained by Professor Blasius 

 that these creatures not merely seek for a change of 

 locality, but that they do so with such regularity that 

 it becomes, in his opinion, a migration. His remarks 

 apply exclusively to a northern species, the Vespertilio 

 borealis of Nilsson, the most southern haunts of which 

 are the mountains of the upper Hartz, and, according 

 to Wagner, those in the vicinity of Regensburgh. It 

 passes, it would appear, northward in the month of 

 August. As it is one of those species, according to 

 Professor Blasius, which come abroad only in the ad- 

 vanced twilight, the most northern part of its range 

 would be unsuitable to its habits " during the hot 

 summer months, when, from the position of the sun, 

 there is no intense twilight, or the sun does not set at 

 all." " It is only," he further remarks, " when, at the 

 advanced time of the year, the dark nights and intense 

 twilight appear, that they arrive with their young in 

 the northern latitudes. Since we know of no instance 

 of specimens in the northern countries having been 

 found in their winter sleep, and the rough weather 

 appearing in the beginning of October, we cannot 



