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lata, and their bodies, in no far as these are similarly 

 formed, can, without injury or inconvenience, bear 

 pressures, crushes, or blows, proportional to what 

 would maim or even destroy the stoutest of the ver- 

 tebrated animals. A beetle, for instance; suffers no 

 injury, by a fall from a height, or the fall of a sub- 

 stance upon it, which, estimating according to the 

 relative weight of the animals, would dash an 

 elephant to pieces, or, at all events, crush it to death ; 

 and the tiny leg of an ant can bear, without the least 

 injury, a pressure, the relative effect of which would 

 crush the paw of a lion to jelly. We shall after- 

 wards have occasion to see that very many of the 

 articulata are, not occasionally only, but habitually 

 exposed to such pressures; and that if they had 

 internal bones and the soft parts outside, they could 

 not exist. 



But the advantages of this structure are as great 

 in action as they are in endurance. The muscles, 

 inserted as they are in the opposite sides of the two 

 jointed pieces, can exert their contractile force, either 

 in bending or straightening the joint, much more 

 effectively than can be done by external muscles, as 

 they have the advantage of the whole lever power on 

 both sides of the joint, and act in the straight line ; 

 while the external muscles very frequently act on the 

 short end of the lever and have, besides, much of their 

 force spent by their acting obliquely, and often through 

 the medium of straps and pulleys, which, smoothly as 

 the working surfaces of animals move upon each 

 other, always destroy some of the power by friction. 

 In the case of the internal muscles (that is, muscles 

 in the inside of the parts which they move), no ten- 

 don, pulley, or ligamentous strap, is required. From 

 the one point of insertion to the other the whole 

 can afford to be efficient contractile fibres ; and as 

 those fibres are also, from their position, able, in 

 almost every imaginable case, to exert the very maxi- 

 mum of their effect, it is not too much to say, that 

 bulk for bulk, or weight for weight, an internal muscle 

 of one of the articulati can act with twice, nay, 

 with ten times the effect of an external muscle in any 

 skeletoned animal. But bulk for bulk, or weight for 

 weight, is not the means by which to .estimate mus- 

 cular activity, nor even a safe element in that esti- 

 mate. Both bulk and weight are in themselves ob- 

 stacles to motion, rather than sources of it ; and in a 

 muscle two pounds in weight there must be one 

 pound of the motive energy expended in moving the 

 additional pound more than would be necessary, if the 

 muscle weighed only one pound. Suppose a certain 

 muscle in an elephant to weigh a quarter of a hun- 

 dred weight, or 28 pounds avoirdupois, and a certain 

 muscle in an ant 1 grain troy ; then, estimating in 

 round numbers the pound avoirdupois at 7000 grains, 

 the relative weights of the muscles will be 196,000 

 for that of the elephant, and 1 for that of the ant. 

 Therefore, the loss of power from the overcoming of 

 the mere inertia in the muscle of the elephant, is 

 nearly two hundred thousand times as great as that in 

 the ant. It must be borne in mind, too, that this over- 

 coming of the inertia of the muscle is not a mere 

 initial resistance, which can be overcome by any mo- 

 mentum after the muscle is in action. The whole 

 body of an animal does acquire a momentum, which, 

 in rapid motion, takes off part of the general weight 

 from the whole organs of motion ; but no single 

 muscle can possibly acquire a momentum which 

 can in any way relieve it of the constant dead- 



v ight of its own inertia. The contractions of a 

 muscle are independent and separate efforts, no one 

 of which transfers the least portion of energy or im- 

 petus to that which follows ; and therefore the inertia, 

 in time, becomes too much for the muscular energy ; 

 and the heavy muscle, when the bodies moved are in 

 proportion, is always first exhausted by fatigue. The 

 large, heavy, and handsome horses, employed in the 

 brewers' drays in London, could not get through one 

 day in a coal-wagon, or a common travelling stage, 

 though for short distances, with rests between, they 

 may pull one-half more than the horses employed in 

 these. 



Another advantage which the internal muscle has 

 over the external one is, that no part of its energy is 

 ever expended in stretching its antagonist. When, 

 for instance, the muscles which bend the human knee, 

 or the joints of the fingers, are exerted, the extensor 

 muscles are pulled in length by the projection of the 

 joint, as it bends, pulling the tendons which pass over 

 it. This, no doubt, keeps the joint steady, but it also 

 diminishes the effect of the flexor muscles in bending 

 the joint. But as the internal muscles pass through 

 the centre of motion, the one of them is not pulled 

 -in length by the contraction of the other ; and there- 

 fore the whole energy of that which contracts is 

 effective in bending the joint. 



The mere fact of being internal, surrounded with 

 fluids, protected from changes of temperature, and 

 from all atmospheric action, is an advantage to the 

 muscles of the articulated animals, which alone would 

 give them considerable additional strength, and 

 especially additional power of continuing in action 

 without fatigue. It would be no easy matter to 

 estimate exactly the effect of the resistance, the de- 

 composing power, and all the other influences of the 

 atmosphere upon external muscles ; arid it would, 

 perhaps, not be more easy to reduce to arithmetic the 

 influence of changes of tempera! ure ; but we feel 

 both, and especially the latter, so much in our own 

 case, as to leave not a doubt that, but for these, we 

 should be both stronger, and less easily fatigued ; and 

 as that is the case with us, we may very safely con- 

 clude that it must be the case with all animals which, 

 like us, have external muscles and internal bones. 



These considerations, and many others which will 

 readily occur to the reader who carefully examines 

 what has been stated, tend to show the advantage, 

 and not the advantage only, but, if the expression 

 may be admitted, the necessity, of the articulated 

 structure in very small animals, which have to make 

 their way along the surface of the ground, or even 

 which sport in the air, as is done by gnats, and many 

 other tiny creatures during almost the whole period 

 of their winged lives. If we were to suppose the 

 mountain rocks shattered into fragments, varying 

 from the size of a haycock to that of our largest 

 buildings, and the whole scattered miscellaneously 

 about, so that in some cases an ox could pass under, 

 and in some others only over them ; if we were to 

 suppose this, and that it were the general character 

 of the earth's surface, then it would bear nearly the 

 same ratio, and oppose nearly the same resistance to 

 the progress of the larger mammalia as the common 

 mould of a garden, with its admixture of pebbles, 

 bears to the size, and opposes to the march of garden 

 ants and the smaller beetles. We have ample proofs, 

 in the smaller obstacles, by which their utmost exer- 

 tions are foiled and defeated, that not even the fleetest 



