THE TRIUMPH OF LilE 



the role of lungs, the breathing organs of land 

 animals. These crabs now Hve in holes in the 

 earth like mice. Only at certain times do they 

 return to their old element: when it is necessary 

 to lay their eggs. The young crabs repeat the 

 history of the race. They breathe water like 

 the poUiwog of the frog, which reproduces once 

 more the fish stage. Sc these land crabs of the 

 palm island teach us the tremendous step which 

 land animals have taken, and at the same time 

 explain the "how" of this step. Along with 

 these crabs there walks a little fish, hopping 

 comically along on its breast fins, climbing at 

 least temporarily^ upon the palm beach, and 

 crawling into the root work of the mangrove 

 bushes to chase insects. This fish has also in a 

 similar manner permitted its gills to revert and 

 dry up, and has begun to breathe air with the 

 attachment that in the water served as a swim 

 bladder. Thus it is that the true lung develops 

 from the air-filled swimming bladder. The air 

 insect, the light-winged dragon-fly, the beauti- 

 ful butterfly, have arisen in this way. Their an- 

 cestors became the lords of the land in the form 

 of crawling worms such as today are numerous 

 in tropical lands. In these many-jointed, man}^- 

 legged worms was developed an ingenious sys- 

 tem of pipes, the so-called tracheal tubrals for 

 breathing air, and this system has been be- 

 queathed to all the descendants. Manifold the 

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