3 2 4 POPULAR SCIENCE MONTHLY. 



level of the field. Besides the moss or grass, they frequently 

 employ coarse wax to form the ceiling of the vault, for the pur- 

 pose of keeping out rain and preventing high winds from destroy- 

 ing it. Within this retreat the eggs present an appearance not 

 very different from that of the bumblebee." 



In conclusion, I may say that among the ancient Hebrews and 

 Romans the error was widely credited that bees made their nests 

 and reared their young in the carcasses of dead animals; and, 

 although these people knew that bees were governed by a ruler, 

 they labored under the impression that it was a king and not a 

 queen. Such ignorance can easily be overlooked, however, when 

 we come to consider that it is only of comparatively recent date 

 that we have worked out the biology of these insects, and, as it is, 

 there yet remains the greater part, by all odds, of their natural 

 history of which we know little or absolutely nothing, and to 

 which must still be added that of the host of species of this order 

 yet to be discovered and made known to science. 



THE PRINCIPLE OF ECONOMY IN EVOLUTION. 



BY EDMUND NOBLE. 



ONE of the many interesting things about evolution, oftener 

 taken for granted than formally recognized, is the fact that 

 the changes which everywhere accompany and constitute it have 

 their rise in a simple excess of pressure in one direction over the 

 pressure in another. For all movement, whether it be of simple 

 or of complex matter, whether it be of an inorganic or an organic 

 system, whether it involve will and conscious perception or not, 

 is in every case and under every conceivable set of circumstances 

 movement in a single mode that is to say, movement in the 

 direction of the least resistance, or from the direction of the 

 greatest traction or stress.* If we look to the origin of the move- 

 ment, we shall speak of acting as in the line of the greatest 

 stress; if we consider the resistances in the presence of which 

 movement is produced, we shall regard acting as in the direction 

 of the least resistance. But, however we may describe it, the 

 truth of the law is obvious, since it follows from the very nature 

 of movement. For if a body be equally stressed from all direc- 

 tions it will not move, while if it be stressed differentially in one 

 direction more than in other directions it will move in the line 

 of, or away from, the greatest stress. Now, as all movement must 



* In order to save repetition, the word " stress " will be used throughout in the sense of 

 traction or stress." 



