ANATOMY AND PHYSIOLOGY 89 



for the differences in weight) for the same reason that a 

 smaller insect has more conspicuous strength than a larger 

 one, when the two are similar in everything except weight. 

 For example: where a bumble bee can pull 16.1 times its own 

 weight, a honey bee can pull 20.2 ; and where the same bumble 

 bee can carry while flying a load 0.63 of its own weight, the 

 honey bee can carry 0.78. Always, as Plateau has shown, the 

 lighter of two insects is the stronger in respect to external 

 manifestations of muscular force in the ratio of this muscu- 

 lar strength to its own weight. 



To understand this, let us assume that a beetle continues to 

 grow (as never happens, of course). As its weight is increas- 

 ing so is its strength but not in the same proportion. For 

 while the weight say that of a muscle increases as the cube 

 of a single dimension, the strength of the muscle (depending 

 solely upon the area of its cross section) is increasing only as 

 the square of one dimension its diameter. Therefore the 

 increase in strength lags behind that of weight more and 

 more; consequently more and more strength is required sim- 

 ply to move the insect itself, and less and less surplus strength 

 remains for carrying additional weight. Thus the larger in- 

 sect is apparently the weaker, though it is actually the 

 stronger, in that its total muscular force is greater. 



The writer uses this explanation to account also for the 

 inability of certain large beetles and other insects to use their 

 wings, though these organs are well developed. Increasing 

 weight (due to a larger supply of reserve food accumulated 

 by the larva) has made such demands upon the muscular 

 power that insufficient strength remains for the purpose of 

 flight. 



Statements such as this are often seen a flea can jump a 

 meter, or six hundred times its own length. Almost needless 

 to say, the length of the body is no criterion of the muscular 

 power of an animal. 



4. NERVOUS SYSTEM 



The central nervous system extends along the median line 

 of the floor of the body as a series of ganglia connected by 



