THE TWIN ISLANDS. 183 



of themselves, sufficient to prove that aestivation is an 

 established habit. "What other evidence among mam- 

 mals have we % 



In August, 1880, 1 found bats on four different occa- 

 sions, all of which were apparently in full health, yet 

 they did not, for some reason, which I supposed to be 

 the excessive heat then prevailing, resume their crepus- 

 cular flights at the usual hour. These bats had " gone to 

 roost " under leaves on trees and a grape-vine, and were, 

 no doubt, fully intending to resume their activity after 

 a nap of a day's length was over. Why did they not ? 

 The following days were excessively hot until the fourth, 

 which was a few degrees cooler. It clouded over early in 

 the afternoon ; soon it became damp, and just before the 

 commencement of a passing shower these bats were 

 stirring a little as they hung — quivering their wings as 

 though to see if all was in working order, and then away 

 they flew, after, in each case, certainly ninety hours of 

 rest. Does it adequately explain all the facts to say that 

 these bats were overcome by the heat ? They were resting 

 in the shade during the day, and the nights, when they 

 would be active, were cooler; but in these cases very 

 little cooler. They were nights to be remembered for 

 their sultriness ; and may it not be that there was not 

 sufficient difference in the mid-day and evening temper- 

 ature to enable them to throw off the nervous prostra- 

 tion caused by the heat of the day ? Explain it thus, and 

 then we are left to consider what is this nervous pros- 

 tration ? In the case of the bats mentioned, they were 

 all in a perfectly torpid state, and gave not the least sign 

 of life when handled, and only flinched slightly when 



