621 



LOCOMOTION OF ANIMALS. 



LOCOMOTION OF ANIMALS. 



522 



The Frog, like the crocodile and tortoise, has not the power of 

 twisting its body ; it moves by a succession of leaps. It is said that 

 the bull-frogs, which are abundant near the great lakes of North 

 America, can leap 6 feet at a bound, and repeat these leaps so rapidly, 

 that they cannot be captured without great difficulty. They will 

 leap over walls 5 feet in height. The hyla, or tree-frog, has each of 

 its toes furnished with a concave disc, which acts as a sucker ; and 

 by this means the animal haa the power of laying hold of the 

 branches of trees with considerable force, and can leap from branch 

 to branch with great agility. It is by means of the hind legs, which 

 are much longer than the anterior, that the body ia projected ; the 

 movements are performed on the same principle as those of the 

 kangaroo and jerboa. 



In descending the scale of organised beings we shall pass from 

 Ophidian reptiles to the Gastropods, such aa the Helices, or Snails, 

 and the Limaces, or Slugs. The movements of these animals are 

 well known to be exceedingly slow. The snail, after creeping from 

 its shell a, expands its body in such a manner that the shell lies 

 poised upon its back (aa in f'j. 44). 



Fig. 44. 



halt, and wait till the cool of the evening. They are sometimes three 

 months in getting to the shore." The order in which the five pairs 

 of lega of the crabs move in walking and running does not appear to 

 have been accurately observed. 



Spiders. The Arachnidce, or Spiders, are furnished with four pairs 

 of legs (the female being provided with an additional pair for the 

 purpose of carrying her eggs). The lega of the different species of 

 spiders vary considerably with regard to length, but the order in 

 which they move appears to be the same. The joint which connects 

 the legs to the body is a kind of ball-and-socket joint, which gives the 

 animal the power of turning the limbs in various directions, but all 

 the other joints of the legs are on the principle of the hinge-joint, 

 thus securing firmness and precision in movement. The extremities 

 terminate in either a single or double hook for the purpose of 

 prehension. 



The apparent complexity of the motions of the limbs of these 

 animals is dissipated by first investigating the order in which they 

 move the legs on one side, and afterwards that of those on the 

 opposite side. By thia means it will be found that the spider 

 advances first the fore leg, then the fourth, then the third, and lastly 

 the second leg ; that is, in the order 1, 4, 3, 2. (F iy. 45). By corn- 

 Fig. 45. 



The shell is carried with the animal in all its perambulations, and 

 the body is withdrawn into it on the slightest alarm, or when in a 

 state of repose, leaving the foot '<', l> only, which ia in contact with 

 the surface on which it treads, without the shell. 



The single foot of the snail is moved by numerous muscular fibres, 

 by means of which it is successively expanded and contracted at 

 various portions of its disc ; so that when one portion of it has 

 advanced, and laid hold of an object on the plane of its motion, the 

 next is drawn forward, and so on in succession, until every portion of 

 the foot has advanced ; but the length of each step ia so small, that 

 the anail takes a long time to walk over a path not more than a foot 

 in length. The movements of slugs are performed in a similar 

 manner, and although they have no house to carry on their back, their 

 progression is also very slow. They appear to move with greatest 

 freedom over vegetable substances, but cannot easily traverse fine 

 loose soils; because the segments of the foot cannot find on such 

 moveable surfaces the requisite fulcrum whereby to drag the body I 

 along. Gardeners avail themselves of this peculiarity to preserve 

 tender plants from their ravages, by strewing loose ashes, or, what is 

 still better, dry sawdust, over the beds. These Gasteropoda aecrete 

 a viscid fluid on their track, which enables them to climb the walls of 

 houses in a vertical path. The adheaive fluid, when dry, reflects the 

 light, so as to present a shining silvery appearance, with which most 

 persons (at least those who live in the country) are familiar. 



Crabs. These animals are, it is well known, inclosed in a solid 

 case, or shell. The body is usually either nearly square or a pear- 

 shaped figure, and the tail is not so long and flexible as in the 

 lobsters. They are furnished with five pairs of legs, which are 

 attached to the under side of the trunk, in that portion of it termed 

 the cephalo-thorax. The hinge-like joints of the legs not having 

 their axes of motion perpendicular, but either parallel, or oblique to 

 the mesial axis of the trunk, they are unable to walk directly 

 forwards, but move on solids either in a lateral or in a retrograde 

 direction. Some species, such as the Land-Crab, or Cancer cursor, run 

 with considerable rapidity. It is even said that they are capable of 

 running with such speed that a man on horseback has great difficulty 

 in keeping pace with them. According to Labat, "these animals 

 not only live in a kind of orderly society in their retreats in the 

 mountains, but regularly once a year march down to the sea-side in 

 a body of some millions at a time. The sea is their destination, and 

 to that they direct their march with right-lined precision. No 

 geometrician could send them to their destined station by a shorter 

 course : they neither turn to the right nor to the left. They will 

 attempt to scale walls to keep the unbroken tenor of their way. 

 They are commonly divided into three battalions, of which the first 

 consists of the boldest and strongest males. These are pioneers, who 

 march forward to clear the route, and to face the greatest dangers. 

 The main body ia composed of females, which never leave the 

 mountains till the rain has set in for some time ; they then descend 

 in columns of 50 paces broad and 3 miles deep. Three or four days 

 after this, the rear-guard follows, consisting of males and females, 

 neither so robust nor so numerous as the fonner. The night ia the 

 chief time of proceeding ; but if it rains by day, they do not fail to 

 profit by the occruion. When the lun in hot, they mnke a universal 



paring this order with that of tho legs on the opposite side, when 

 acting simultaneously, it will be found that they begin by moving 

 the first right leg, then the fourth left; then follow the first left, and 

 the fourth right ; then the third right, and the second left. The first 

 two sets of lega are thus moved consecutively in the order 1', 4, 1, 4', 

 a mode of progression which resembles that of quadrupeds : the 

 remaining legs move in pairs simultaneously, namely, 3', 2, and 3, 2' ; 

 and thus it ia found that whilst the legs of one side of the animal 

 are moving consecutively, in the order 1, 2, 3, 4, the legs of the other 

 side are moving in pairs, in the order 4', 1', 2', 3'. Most persons are 

 aware of the facility with which spiders spin the beautiful but fragile 

 cord, by means of which they safely descend from heights that would 

 be fatal to larger animals unprovided with some means of breaking 

 the shock which would result from a fall from such elevations. In 

 descending their newly-spun thread, they suspend the body to it by 

 one of the hind legs : on returning by the same thread, they make 

 use of three legs, the first two on one side, and the first or second on 

 the other. The spider is endowed with the power of running with 

 considerable speed on its web, in the chace and capture of its insect 

 prey ; and is capable of leaping a considerable distance, many times 

 its own length. It throws its thread across chasms, and thereby 

 forms for itself a suspension-bridge in an incredibly shorter period 

 of time than our most celebrated engineers are capable of accom- 

 plishing; thus showing that, inferior as the spider is to man in 

 strength and organisation, it has yet been amply provided by an all- 

 watchful and omnipotent Creator with the means of transporting itself 

 from place to place, and of procuring its sustenance. The same 

 cordage which serves to give it a ready passage across cavities which 

 could not otherwise be traversed without great labour aud expenditure 

 of time, serves also as the best material with which to weave its net 

 for entrapping its prey. 



Insects. Many insects are endowed with the triple powers of walk- 

 ing, running, and leaping on solids; of flying in the air like birds; and 

 of swimming in water like fishes. For these manifold purposes it is 

 obvious that they must possess a peculiar organisation. To enable 

 them to move on solids they are furnished with six legs : the first pair 

 is attached to that part of the trunk called the prothorax ; the second 

 pair to the mesothorax ; and the third pair to the metathorax, which 

 ia the last segment of the thorax. In some insects the legs are arti- 

 culated to the trunk by a ball-and-socket joint ; in others by a hinge- 



