70 ENTOMOLOGY 



spongioplasm (anisotropic) embedded in a matrix of clear, semi-fluid, 

 nutritive hyaloplasm (iso tropic). The spongioplasmic threads of the 

 long bands extend longitudinally and those of the short bands ("Krause's 

 membrane") radially, in respect to the form of the fiber. Moreover, the 

 attenuated extremities of the longitudinal fibrillae connect with the radial 

 nbrillae, the points of connection being marked by slight thickenings, or 

 nodes, which go to make up Krause's membrane. 



Under nervous stimulus a muscle shortens and thickens because its 

 component fibers do, and this in turn is attributed to the shortening and 

 thickening of the longitudinal fibrillae. When the stimulus ceases, the 

 radial nbrillae, by their elasticity, possibly pull the longitudinal ones back 

 into place. The last word has not been said, however, upon this per- 

 plexing subject. 



Muscular Power. The muscular exploits of insects appear to be 

 marvellous beside those of larger animals, though they are often exag- 

 gerated in popular writings. The weakest insects, according to Plateau, 

 can pull five times their own weight and the average insect, over twenty 

 times its weight, while Donacia (Chrysomelidae) can pull 42.7 times its 

 weight. As contrasted with these feats, a man can pull in the same fash- 

 ion but .86 of his weight and a horse from .5 to .83. How are these dif- 

 ferences explained? 



It is incorrect to say that the muscles of insects are stronger than those 

 of vertebrates, for, as a matter of fact, the contractile force of a vertebrate 

 muscle is greater than that of an insect muscle, other things being equal. 

 The apparently greater strength of an insect in proportion to its weight is 

 accounted for in several ways. The specific gravity of chitin is less than 

 that of bone, though it varies greatly in both substances. Furthermore, 

 the external skeleton permits muscular attachments of the most advan- 

 tageous kind as compared with the internal skeleton, so that the muscles 

 of insects surpass those of vertebrates as regards leverage. These reasons 

 are only of minor importance, however. Small animals in general appear 

 to be stronger than larger animals (allowing 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. Al- 

 ways, 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 

 muscular strength to its own weight. 



