Origin of Different Kinds of Adaptations 343 



problem as to whether the flowers, being lateral in position, 

 have assumed a bilateral form because their internal re- 

 lations were bilateral ; or whether an external relation, for 

 example, the visits of insects, has been the principle cause 

 of their becoming bilateral. 



Fig. 4. — A, right and left claws of lobster ; B, of the fiddler-crab ; and C, 



of Alpheus. 



In some bilateral forms the right and left sides may be 

 unsymmetrical in certain organs. Right and left handedness 

 in man is the most familiar example, although the structural 

 difference on which this rests is not very obvious. More 

 striking is the difference in the two big claws of the lobster 

 (Fig. 4 A). One of the two claws is flat and has a fine saw- 

 toothed edge. The other is thicker and has rounded knobs 

 instead of teeth. It is said that these two claws are used by 

 the lobster for different purposes, — the heavy one for crush- 

 ing and for holding on, and the narrower for cutting up the 



