TWO CITIZEN CRABS OF NONSUCH 



her deliberate and mysterious manner remolds the 

 webs into palms and the rays into fingers, and the 

 mental adjustment to the new habit and habitat 

 is consolidated by the all-important physical one. 

 Planes' ancestors as Cliff Dwellers needed only 

 thin legs and ankles, and Planes as a Weed Climber 

 would hardly need any radical change, no more 

 than a rock-living baboon would require among 

 swaying, yielding branches. But when one's whole 

 material world is afloat, and subject to constant 

 buffeting and upsetting by waves it would go hard 

 with the first crab fitted with mountain-climbing 

 legs when hurled off his vegetable raft. On the other 

 hand if Nature had done the obvious thing and pro- 

 vided him with broad, spatulate, oarlike swimming 

 legs, he would be as much at home in the interstices 

 of the weed as a bat in a tangled thicket, or spaghetti 

 on a spoon. 



We find a clever compromise. The posterior legs 

 of Planes are very slightly flattened, muscle being 

 hardly needed in traversing weed under water. 

 Four fathoms down I can pull myself through coral 

 branches with a crooked finger, whereas in a tree, 

 both hands and feet are necessary for progress. And 

 along the anterior surface of each of the limbs of 

 Planes is a broad, bladelike row of feather hairs, 

 slender stems like pliable spun glass with innumer- 

 able short barbs, interlocking, yet lying down at a 

 touch when pressed endwise. They offer no resist- 

 ance when their owner is creeping through the 

 tangled foHage, but when a sudden wave projects 



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