5IO POPULAR SCIENCE MONTHLY. 



tain favorable attractive conditions, to escape more dominant forms 

 outside, or simply by chance, from being carried in streams of water 

 into these subterranean cavities, the result has been the same for all, 

 and their return to the struggle carried on by their ancestors out of 

 the question. They are distinct species modified and adapted to this 

 particular environment where survival is possible, but opportunity for 

 progressive evolution too limited to permit of advance. 



Along the path of protective devices, mimicry, adaptive coloration, 

 form and habit have traveled a host of different forms — flies that look 

 like bumblebees and thereby gain entrance to their nests to provide 

 extra food for their larvae; butterflies that look like leaves of trees; 

 leaf insects (phasmids) so like the leaves they live upon as to be invisi- 

 ble to foes ; bugs that look like ants ; scale insects that look like excres- 

 cences on the bark of the trees they infest; edible species that have 

 taken form and color of inedible species; toads that look like lumps 

 of earth; frogs that look like green scum or leaf at water side; snakes 

 and lizards in great numbers that resemble the soil on which they live; 

 birds that so closely imitate the colors of earth, foliage or irregulari- 

 ties of bark as to escape observation — in fact, an unending train in 

 varying degrees, furnishing a most fascinating field for study. 



Among aquatic animals we have fishes that hug close to the bottom 

 and acquire color and pattern which admirably protect them, and the 

 flounder has even gone to such an extreme in this direction as to have 

 one of its eyes transferred from its normal position to the opposite side 

 of the head. Skates and rays have the same flattening, but retain their 

 normal position. Other fishes resemble rocks and so perfectly as to be 

 practically invisible. Others, like sea horses, resemble parts of sea 

 weed, streaming in the currents of water or branches of coral to which 

 they cling. Mollusks and crustaceans adopt this plan to make them- 

 selves inconspicuous, and the different devices shown would fill a 

 volume. Perhaps no stranger combination is presented than in the 

 little crab which makes its home in a mollusk shell, but not content 

 with this protection conspires with a sea anemone to take root upon its 

 house top and add the variety of its structure to the deception. A 

 queer sight these anemones, nodding here and there as borne by a hidden 

 crab. 



Most animals aside from man have been content to let electricity 

 alone, and we are inclined to think the use of this magical force in 

 nature of very recent origin. However, some of the aquatic animals, 

 at least, and these forms that must have had their origin in the long, 

 long ago of geological time, have brought to their use this elusive force 

 and present in the structure of their organs for the generation of elec- 

 tricity some quite remarkable parallels to the electric apparatus of 

 human invention. In such lines we have the torpedo, a broad, flat. 



