THE MUSCLES ; THE FAT-BODY AXD CCELOM. 83 



low in comparison with that of Vertebrate muscles. The abso- 

 lute force of the adductor muscles closing a bivalve shell may, 

 in certain Lamellibranchs, equal that of the most powerful 

 Mammalian muscles ; in others it falls below that of the least 

 powerful muscles of the frog, which are greatly inferior in 

 contractile force to Mammalian muscles. We find, therefore, 

 that the low contractile force of Insect muscles is in harmony, 

 and not in contrast, with common observation of their physical 

 properties, and that the high relative muscular force, correctly 

 enough attributed to them, is explicable by considerations which 

 apply equally well to models or other artificial structures. 



The comparison between the muscular force of Insects and 

 large animals is sometimes made in another way. For example, 

 in Carpenter's Zoology* the spring of the Cheese-hopper is 

 described, and we are told that " the height of the leap is often 

 from twenty to thirty times the length of the body ; exhibiting 

 an energy of motion which is particularly remarkable in the 

 soft larva of an Insect. A Viper, if endowed with similar 

 powers, would throw itself nearly a hundred feet from the 

 ground." It is here implied that the equation 



Height of Insect's leap Supposed ht. of Viper's leap (100 ft.) 

 Length of Insect Length of Viper 



should hold if the two animals were " endowed with similar 

 powers." 



But it is known that the work done by contraction of muscles 

 'of the same kind is proportional to the volume of the muscles 

 (" Borelli's Law"),f and in similar animals the muscular 

 volumes are as the weights. Therefore the equation 



Work of Insect Work of Viper 

 Weight of Insect Weight of Viper 



will more truly represent the imaginary case of equal leaping 

 power. But the work = weight raised X height, and the weight 

 raised is in both cases the weight of the animal itself. Therefore 



Wt. x Ht. Wt. x Ht. 



^\vtT " ( Insect ) : "WtT " ^ lper )' 



' Vol. II., p. 203. The calculation here quoted is based upon an observation of 

 Swammerdam, who relates that a Cheese-hopper, 5 in. long, leaped out of a box 

 6 in. deep. 



t Haughton's Animal Mechanics, 2nd ed., p. 43. 



