128 HIBERNATION OF THE BATS. 



fact, the animal heat of these creatures is rather high, as is the case with most flying 

 beings, whether mammals or birds. 



Many curious and valuable trials have been made upon bats while in a state of torpid- 

 ity, the subjects of experiment being placed in such a manner that the least act of 

 respiration made itself clearly visible, by the movements of a delicate index. The 

 wing was extended in such a manner, that the circulation of the blood was perceptible 

 through its semi-transparent membrane, and a thermometer was arranged so as to 

 register the temperature. 



Very great care is requisite in conducting these experiments, because the least 

 excitement, or the slightest raising of the temperature, suffices to rouse the somnolent 

 animal, and to alter the conditions which are absolutely necessary for true hiberna- 

 tion. A hasty footfall, or an accidental tap given to the table on which the creature 

 rested, would cause it to make several respirations, and to recover sufficient vitality to 

 raise the temperature, and to consume some portion of oxygen from the air. The same 

 animal which passed ten hours in a state of perfect somnolence, without producing any 

 perceptible effect on the oxygen contained in the atmospheric air, consumed in a single 

 hour more than four cubic inches of oxygen, when aroused and lively. 



The curious subject of hibernation will be again noticed in connection with the various" 

 animals, such as the marmot, dormouse, and others, which pass the cool months in a 

 state of torpidity. 



The analogy that exists between the bats arid the birds is too evident to escape 

 attention. But the most curious part of the analogy is the order in which the various 

 portions of a mammalian animal are modified, so as to discharge the faculties which 

 belong more properly to the feathered tribes. 



The elongation of the fingers, and expansion of the membranous " wings," has 

 already been mentioned, as well as the general development of the breast-bone. These 

 two structures are in common with all bats, as are their corresponding portions in all 

 birds. But there are some organizations which are found greatly developed in certain 

 families of birds, and are repeated in certain of the bats. 



The structure to which allusion is here made is that connection of the lungs with the 

 skin, or, rather, with the space between the skin and the body, that is found in many 

 birds, especially those which pass a marine existence, and which enables the bird to 

 inflate its skin with air, and so to increase its bulk largely without sensibly increasing 

 its weight. 



In the birds, this inflation is made by direct communication with the lungs ; but in 

 the bat, the air is conveyed into the membranous cells after a different fashion. A very 

 small opening is found to exist at the bottom of the cheek-pouches of either side, and is 

 furnished by an apparatus by means of which the air is prevented from escaping without 

 the will of the animal. This opening affords a communication between the mouth of 

 the bat and the space beteen the skin and flesh, which are only tied to each other by 

 a few membranous threads at each side of the neck, and on the sides of the thumb. 



When, therefore, the bat desires to inflate its body, it closes its mouth, and forces 

 the air from -its lungs through these cheek passages into the empty space between the 

 skin and flesh. The result of this operation is, that the skin is puffed out on all sides 

 of the animal, so that the creature is immersed in a kind of atmospheric bath. So 

 enormously is it distended by the amount of air which is introduced, that it loses all 

 its shapely proportions, and looks like a little ball of fur, to which the head and limbs 

 had been artificially attached. 



The bats which are possessed of this wonderful faculty belong to the genus "Nycteris," 

 and are found in Africa. What may be the object of so singular a power is not satis- 

 factorily proved. That it gives very great buoyancy to the form is evident enough 

 but it also seems plain that it is intended for other designs than the obvious one of 

 decreasing the proportionate weight of the animal 



