66 THE EVOLUTIONIST AT LARGE. 



strongest flesh. The crab, on the other 

 hand, lives on the sandy bottom, and walks 

 about on its lesser legs, instead of swimming 

 or darting through the water by blows of its 

 tail, like the lobster or the still more active 

 prawn and shrimp. Hence the crab's tail 

 has dwindled away to a mere useless his- 

 torical relic, while the most important muscles 

 in its body are those seated in the network 

 of shell just above its locomotive legs. In 

 this case, again, it is clear that the appendage 

 has disappeared because the owner had no 

 further use for it. Indeed, if one looks 

 through all nature, one will find the philo- 

 sophy of tails eminently simple and utili- 

 tarian. Those animals that need them 

 evolve them ; those animals that do not need 

 them never develop them ; and those animals 

 that have once had them, but no longer use 

 them for practical purposes, retain a mere 

 shrivelled rudiment as a lingering reminis- 

 cence of their original habits. 



