BATS. 9 



suppose that they remain for more than six weeks until 

 they return to their southern winter quarters." 



Professor Blasius leaves us in doubt respecting the 

 hibernation of this species after it has returned to its 

 winter quarters, but the following remarks, in addition 

 to those we have already quoted, are too interesting to 

 be omitted : 



" If we determine," he continues, " their usual habi- 

 tation, where they bring up their young, to be between 

 54 and 58 N. lat., and the supposed northern limit of 

 their distribution to be about 68 to 70 N. lat., the 

 result is a change of habitation of at least 10 degrees of 

 latitude. 



" This change of locality is the only ascertained fact 

 in the mode of life of these Bats, and it may be com- 

 pared with the migration of birds. Although we may 

 be able to trace in the Hartz and other German mountains 

 a wandering of allied species from the plain to the 

 mountains, yet such a change extends only a few miles, 

 and is measured by days and not by months. A striking 

 difference between the migration of Birds and Bats is, 

 that while the former move northward for the purpose 

 of breeding, the latter arrive there only after they have 

 grown-up young ones." 



In this country, where, so far as we know, no change 

 of habitat takes place, constant observation has shown 

 that some species come abroad early in the evening, and 

 others late, a given degree of light being necessary for 

 each. May we not suppose that the migration of Bats 

 observed by Professor Blasius was the mere unconscious 

 appearance, night after night, of these creatures at a 

 spot somewhat removed from that of the previous 

 night, thus following the twilight, rather than what 

 may be properly termed as migration ? But the hiber- 



