128 



KNOWLEDGE 



[July 1, 1891. 



be a dtcided improvement on the eaiiy type, it seems, 

 indeed, that in all groups of Vertebrates capable of true 

 flight a long tail has been found disadvantageous, since 

 among tlie Pterodactyles the more specialised kinds found 

 in Europe had discarded the long tail of the species repre- 

 sented in Fig. 3 ; and the same holds good with regard to 

 the lai'ge toothless kinds found in the cretaceous rocks of 

 the United States. Again, the most specialised, or in- 

 sectivorous Bats are remarkable for the shortness of their 

 tails. From the relative shortness of its wings, coupled 

 with the long unwieldy tail, it is probable that the 

 Archipopteryx was but a poor flyer, and was, perhaps, 

 altogether incapable of making the long-sustained flights 

 of our modern birds, though it must undoubtedly have 

 been a true flyer. 



Birds vary greatly in the relative proportions of the 

 component bones of the wing, so that among the 

 strongest flyers we find that whereas in the giant Alba- 

 tross of the tropical seas the bones of both the upper and 

 fore-arm are enormously elongated, in the Swift that of 

 the upper arm is so shortened and thickened as to be 

 scarcely recognisable. The form and arrangement of the 

 flight -feathers are, however, of still greater importance in 

 modifying the shape of the wing, but the reader desirous 

 of information on this subject must consult one of the 

 numerous works on the structure of birds. 



Coming now to the highest class of animals, the 

 Mammals, we shall find that while true flight is only 

 possessed by the whole of the members of a single order, 

 spurious flight occurs among certain members of three 

 widely distinct oraers ; and it is curious to notice the re- 

 markable external similarity between some of these 

 animals possessing the power of spurious flight, while 

 they are structurally so difl'erent from one another. 



Commencing with spurious flight, the first Mammals 

 we have to mention are the Flying Phalangers of 

 Australia, which belong to the great order of Pouched or 

 Marsupial Mammals, described in a previous number of 

 Knowledge, and are closely allied to the so-called Opossums 

 of the colonists. There are several genera of these curious 

 and beautiful creatures, distinguished from one another by 

 the character of the skull and the shape of the parachute, 

 which may be either very broad or very narrow. This 

 parachute consists of an expansion of the skin of the sides 

 of the body, extending from the wrist of the fore-leg to 

 the ankle of the hind-leg, with a smaller development 

 between the neck and the front of the fore-leg. The 

 Flying Phalangers are strictly nocturnal in their habits, 

 and are able to take enormous flying leaps fi-om tree to 

 tree, during which they descend in the first part of their 

 course, but acquire a slightly upward direction before they 

 alight. 



It is not till We come to the order of Rodents, or those 

 Mammals which, like Hares, Eats, and Beavers, are 

 provided with a pair of chisel-like gnawing-teeth in the 

 front of each jaw, that we again meet with Mammals 

 having the power of spurious flight. Among the most 

 curious of these are the so-called Anomalures of Africa, 

 which are small Rodents nearly related to the Squirrels. 

 Here we find the parachute connecting both pairs of 

 limbs together, as in the Flying Phalangers, but with the 

 additional jieculiarity that there is a spike-like rod of 

 cartilage projecting from the elbow, which, by acting in 

 the manner of a yard-arm, allows the width of the expan- 

 sion to be greater than could otherwise be the case. This 

 rod, together with tiie presence of a series of scales along 

 the sides of the base of the tail — from which the creatures 

 take their name — serves to distinguish the Anomalures 

 from the Flying Squirrels. Of the latter there are three 



genera, mostly found in the oriental region, although a few 

 species range into North America and Europe. These 

 creatures exactly resemble ordinary Squirrels in general 

 appearance and habits, with the exception of haWng a 

 parachute connecting the front with the hind limbs, after 

 the manner of the Flying Phalangers. In some species 

 an additional membrane connects the root of the tail with 

 the thigh, but this is wanting in others. The flight of the 

 Flying Squirrels is precisely like that of the Flying Pha- 

 langers ; and if the two were to be found together, it would 

 be quite impossible to distinguish the one from the other 

 dijring flight. Flying Squirrels, however, utter a sharp, 

 squeaking cry during their flight, while the Flying Pha- 

 langers appear to be silent. Ordinary Squirrels, as we all 

 know, are capable of taking long leaps from bough to 

 bough, and in the Flying Squirrel it is merely an excess 

 of this power which, owing to the development of the 

 parachute, assumes the character of flight. A precisely 

 similar connection obtains between the ordinary Phalangers 

 and the Flying Phalangers. There are a large number 

 of species of Flying Squirrels, which are mostly of com- 

 paratively small size, altliough one species, from the north- 

 west of Kashmir, is as large as a rabbit. Although their 

 cries may frequently be heard at night in the districts 

 which they inhabit, Flying Squirrels are but seldom seen. 

 Their flight may be extended to a distance of twenty-five 

 or thirty yards. 



The Flying Lemurs, of the Malay Peninsula and the 

 PhiUppines, present a type of Mammal in which the 

 facility of spurious flight has attained its maximum of 

 development. These animals come nearest, in general 

 structure, to the so-called Insectivorous Mammals, such 

 as the Mole, Shrew, and Hedgehog, and are, therefore, 

 usually regarded as forming an aberrant group of that 

 order. In them not only are the fore and hind limbs of 

 either side connected together by an expansion of the skin 

 of the sides to form a parachute, but the expansion of the 

 skin also extends backwards between the hind legs, which 

 it connects with the long tail completely up to its tip. 

 Moreover, although the fingers and toes are only of the 

 ordinary length, yet they also are connected by a mem- 

 brane, in the manner of the webbed foot of a duck. At 

 night, during which time they become active, the Flying 

 Lemurs will take flights of upwards of seventy yards in 

 length, and thus far outrival the Flying Squirrels and 

 Phalangers in this respect. Bats, as we shall notice 

 shortly, are known to be closely allied to the Insectivores, 

 and the Flying Lemur seems to show us how an ordinary 

 Insectivore may have become gradually modified into a 

 Bat ; for it would only require the elongation of the 

 fingers and a somewhat greater development of the para- 

 chute to transform the Flying Lemur into a creature 

 exceedingly like a Bat. 



Bats, which are familiar to all of us, are the only 

 Mammals endued with the power of true flight ; and 

 although they are evidently related, as shown, among 

 other features, by the structure of their teeth, to the 

 Insectivores, yet they are so difiereut as to be entitled to 

 rank as a separate order by themselves. In being the 

 only truly flying Mammals they hold, as has been well 

 observed, a position in the class precisely analogous to 

 that occupied among the Reptiles by the Pterodactyles. 

 That they have, however, no sort of connection with the 

 latter group is perfectly evident from the structure of the 

 fore-limb, or wing, which we now proceed to explain. 



The wing of a Bat is composed of a thin naked mem- 

 brane supported by a great extension of the bones of the 

 fore-limb ; this membrane being continued backwards to 

 connect the hind-legs with the whole length of the tail. 



