GENERAL CHARACTERISTICS. 



99 



in these respects, hibernate. In tropical 

 countries they are active all the year round. 



For their winter retreats the bats seek out 

 warm dark recesses sheltered from the wind, 

 and in these they are often found together in 

 enormous swarms. Caves, grottoes, clefts in 

 the rocks, hollow trees, retired corners in 

 buildings, unused chimneys, the spaces be- 

 neath roofs, and so forth are the places 

 where they are chiefly to be found during 

 this period of the year. Among buildings 

 they naturally prefer old disused buildings 

 where people seldom come. Such winter- 

 quarters are often sought out by bats from 

 distant parts all round. The different species 

 mostly hang themselves up separately. The 

 hardier forms, which have less dread of the 

 cold, fly out earlier in the spring, and return 

 later in the autumn, and place themselves 

 nearer the entrances to the caves, while the 

 other species retire further in. Before the 

 beginning of the winter-sleep copious evacua- 

 tions take place, and then the animals hang 

 themselves up by the claws of the hind-feet 

 with the head downward, and more or less 

 enveloped by the wings. This occupation 

 of the winter-quarters is not effected without 

 a good deal of quarrelling, crying, and even 

 biting. Frequently they even hang on by 

 one another. As in all hibernating animals, 

 the temperature gradually sinks, and the 

 body, at first fat, becomes thin; the beats of 

 the heart and the movements of respiration 

 become less frequent, and consciousness is 

 often lost to such an extent that the animals 

 cannot be awakened except by warmth. Yet 

 in this respect different species are very 

 different from one another. Some have a 

 comparatively light sleep, waking up again 

 when there is but a slight rise of temperature, 

 and sometimes even flying out, or changing 

 their position, not without quarrelling. Others 

 again sleep much more profoundly. In such 

 winter-quarters the excrement of bats, in 

 which are always to be found undigested re- 

 mains of insects, legs, carapaces, wing-covers, 



«&c., is heaped up to the depth of a foot or 

 more, so that the accumulation can be em- 

 ployed as guano. During the hibernation 

 the functions of the body, in particular the 

 breathing, take place at the expense of the 

 stored-up fat. 



Frequently these winter-quarters are used 

 by the bats as retreats by day, even during 

 their period of activity in summer; but, for the 

 most part, other summer-quarters are sought 

 out, often at a great distance from those oc- 

 cupied during the winter, and then they are 

 mostly occupied only by individuals of the 

 same sex. Thus I once examined at Geneva 

 retreats of the early -flying noctule, which 

 were inhabited only by males, with only a 

 female here and there, and which duringf the 

 winter regularly stood empty. In taking oft' 

 the roof of a six -storied house, to the space 

 beneath which access could be obtained by 

 only a single hole, from which the bats could 

 be seen regularly flying out, so that there 

 could be no difficulty in keeping all the oc- 

 cupants prisoners, seventy males were found 

 with only two females. While in summer the 

 noctule hunts about in the town of Geneva, 

 and makes its retreats in corners about houses, 

 one would seek for it there in vain in winter, 

 since it then prefers hollow trees. 



There is much that is peculiar in the mode 

 of reproduction of these animals. The 

 uterus is always partially divided, sometimes 

 divided almost throughout its length, but, for 

 the most part, as In birds, though not to the 

 same extent as In them, the ovary and the 

 horn or prolongation of the uterus on one 

 side are Imperfectly developed, so that the 

 internal organs are not symmetrical. Most 

 species bring forth only one young one at a 

 time, but many frequently two. At the time 

 of giving birth to her young the female sus- 

 pends herself by the claws of the thumbs, 

 and bending the tail inwards forms a sort of 

 sack with the lower portion of the flying 

 membrane, and into this drops her young. 

 In the case of the horseshoe-bat the young 



