268 OUR HOUSEHOLD INSECTS 



than human beings, horses, or other large animals, such 

 advantage does not necessarily proceed from any supe- 

 riority in the quality of their muscles, but simply from 

 their being so much smaller. And further than this, if 

 their muscles were really as good as those of vertebrates, 

 they ought, in accordance with the above calculation, to 

 be far stronger than they are. Their " absolute muscular 

 force," indeed, as Plateau terms it, is low in comparison 

 with that of higher animals, although their " relative 

 muscular force " is extremely high. So, then, if we were 

 to magnify the dimensions of our flea, without altering 

 the character and quality of its muscular fibres, we 

 should gradually lessen its relative strength, and, by 

 the time it had reached human proportions, it would 

 have turned out to be a far inferior animal. This 

 somewhat complex subject may be found more fully 

 discussed in Miall and Denny's excellent work on the 

 " Cockroach," from which the above illustrations are in 

 substance derived, and to which those who wish to 

 pursue the subject further are referred. 



In this connection, a passing reference may be made 

 to the so-called educated or performing fleas, which have 

 sometimes been exhibited in different places. The chief 

 difficulty met with in the training of fleas is, it seems, to 

 restrain them from jumping, and to induce them to walk 

 in an even and regular manner. One of the methods of 

 overcoming this tendency to sprightliness is to imprison 

 them in circular glass-topped boxes which are kept re- 

 volving : every leap they take brings retribution in the 

 shape of violent collision with the sides of their cell; 

 and, as they are at the same time dazed, it is believed, 

 by the movement of the box, they seem to get tired of 

 this unpleasant experience, and, after a while, cease leap- 

 ing, and settle down to a steady walk. Mr. W. H. Dall, 



