88 ENTOMOLOGY 



hyaloplasm (isotropic). 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 longi- 

 tudinal fibrillae connect with the radial fibrillae, 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 fibrillae, by their elas- 

 ticity, possibly pull the longitudinal ones back into place. The 

 last word has not been said, however, upon this perplexing 

 subject. 



Muscular Power. The muscular exploits of insects appear 

 to be marvellous beside those of larger animals, though they 

 are often exaggerated in popular writings. The weakest in- 

 sects, 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 

 fashion but .86 of his weight and a horse from .5 to .83. How 

 are these differences explained? 



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

 than those of vertebrates, for, as a matter of fact, the contrac- 

 tile force of a vertebrate muscle is greater than that of an 

 insect muscle, other things being equal. The apparently 

 greater strength of ah 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 sub- 

 stances. Furthermore, the external skeleton permits muscu- 

 lar attachments of the most advantageous kind as compared 

 with the internal skeleton, so that the muscles of insects sur- 

 pass 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 



