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 
