LOCOMOTION OF ANIMALS IN AIR. 189 



respiratory movements ; other species simply float in the water by means of 

 hollow air-floats or vesicles (Physalia, Portuguese man-of-war), a method of 

 progression called physograde ; or they have a syringograde mode of progres- 

 sion ; or, lastly, they move by means of rows of very large ciliograde, as in 

 Beroe, Cydipus. 



The ciliograde mode of progression is also invariably employed in the swim- 

 ming acts of the Protozoa, a's in the infusoria, and in the gemmae of sponges. 



Locomotion of Man in Air. 



This is impossible, except as the result of impulses obtained from 

 solid supports, combined with the effects of gravity. The extraordi- 

 nary agile, graceful, easy and perfect acrobatic movements of the 

 celebrated Leotard are thus performed, and surpass in elegance the 

 similarly executed movements of the spider, monkey, and of other 

 arboreal and so-called flying mammalia. 



Locomotion of Animals in the Air. 



Flight, in its highest perfection, is a movement limited amongst the Verte- 

 brata to Birds, and in the Annulosa to Insects. Amongst the Mammalia, 

 however, the comparatively feebly flying bats are found. Certain examples 

 are also seen, as in the flying lemurs and squirrels, of a parachute mode of de- 

 scent in the air, which cannot be called flight, for such animals are unable to 

 ascend, or even to move horizontally in that medium ; the source of movement 

 in them is their gravity, the direction of the action of which is altered by the 

 membranous expansions passing from one limb to the other, which are 

 stretched by the spreading out of their fore and hind limbs. In the bats 

 there is a true power of flight, but it is imperfect in comparison with that of 

 birds, being short in its duration, low in reference to the earth, irregular and 

 fluttering in its character, and incapable of being performed in very gusty 

 weather, or in rain, which drenches the hair and wings of the animal, and so 

 impedes its movement : bats chiefly inhabit temperate climes, and limit their 

 appearance on the wing to serene evenings and nights. The sternum of the 

 bat is proportionately large, and developed downwards into a slight keel for 

 the attachment of a pectoral muscle, which is larger in comparison with the 

 body, than in any other Mammalia ; their clavicles and scapulae are strong, 

 to afford resistance to the drawing inwards of the shoulders in flight ; the arm 

 and fore-arm are elongated, and so especially are the metacarpal bones and 

 phalanges of the three outer fingers, between which the web-like expansion of 

 the wings is stretched. This web always extends the whole length of the 

 trunk, backwards to the short, hinder limb, excluding the foot ; and some- 

 times it is continued on to an elongated coccyx or tail, which is used as an 

 effective rudder. The foot, free from the web, is used for prehensile pur- 

 poses, the bat hanging with its head downwards, and even sleeping, and in 

 cold climates hibernating, in that position. In the fore-limb or hand the 

 thumb is also free, and hooked as a prehensile instrument. The pectoral 

 and other muscles of the fore-limb are very largely developed. 



Passing over Birds to Reptiles, we have to select as examples of true, though 

 probably of awkward flight, the extraordinary extinct flying reptiles (pterodac- 

 tyles, &c.), the formation of the sternum and upper limbs of which sufficiently 

 indicates the manner in which they were used, but leads to the inference that 

 their flight was probably merely an occasional mode of progression, sustainable 

 for short intervals only. Amongst the living reptiles, the little so-called flying 

 lizard or dragon, affords an example of the parachute mode of progression ; its 

 lateral membranous expansions are supported by bony processes belonging to 

 the lumbar vertebrae, sometimes named false ribs, but placed altogether behind 

 the proper thorax ; these membranes are capable of being shut up, owing to 

 the movableness of the bony processes which support them ; and they are ex- 



