1899.] Ai,cock. — The Natural History of Irish Bats, 33 



As a rule, members of the genus Vespertilio are said to 

 retire sooner and come out later than members of the genus 

 Vespcnigo. 



Thus, the Pipistrelle (in England) comes out in March, 

 and retires in November or December (Tomes, xvii.), the 

 Whiskered Bat appears in April and retires about September 

 or October. 



The Noctule appears on March 12 (Tomes), May 1st 

 (Borrer) ; it retires on September 18 (Tomes) ; September 18, 

 in Cheshire, September 22, in Devonshire, October 1st, in 

 Surrey (Coward). 



The time is apparently not always the same in England 

 and Ireland, for instance Mr. Coward has not observed 

 Daubenton's Bat in Cheshire after August 17 ; in Co, Wicklow 

 I have seen this species as late as September 26, and Mr. 

 E. B. Knox has seen it in Co. Cavan on September 23rd. 



Many researches have been made into the cause of hiber- 

 nation, and though this is still a debated point much infor- 

 mation has been gathered. Hibernation is found among 

 isolated members of such different groups as Mammalia, 

 Reptilia, Insecta, and Mollusca, Aves forming a remarkable 

 exception. 



When one of these animals, a bat for instance, intends to 

 hibernate, the following phenomena are observed. The 

 animal retires to a secluded spot, hangs itself up, and 

 gradually becomes motionless. Its temperature falls to 

 within a few degrees of the surrounding air, and its breathing 

 becomes shallow and irregular — " Cheyne Stokes" in type. 

 If accurate measurements are taken, it is noticed that much 

 more oxygen is absorbed than is accounted for by the 

 carbonic acid given out, so that the animal actually gains in 

 weight. The heart beats more slowly and less forcibly, and 

 the activity of the nervous system is much reduced. 



On awakening from this condition in the spring, these 

 phenomena are reversed. The animal's temperature rises, 

 sometimes as much as 31 in 15 minutes. The muscles 

 shudder convulsively, the heart beats more strongly, and the 

 skin, before pale, assumes a rosy blush. Respiration becomes 

 more rapid, and there is a great discharge of carbonic acid 

 from the lungs. 



