THE ELEMENTS OF MIND 203 



herd of vicunas were closely pursued the strong 

 males covered the retreat of the weaker and less 

 swift members of the herd by lagging behind and 

 protecting them (20). 



A remarkable instance of altruism which he 

 once saw exhibited by the king-crabs in a London 

 aquarium is mentioned by Kropotkin in his work 

 on * Mutual Aid a Factor in Evolution.' One of 

 these crabs had fallen on its back in a corner of 

 the tank. And for one of these great creatures, 

 with its saucepan carapace, to get on its back 

 is, even in favourable circumstances, a serious 

 matter. The seriousness was increased in this 

 instance by an iron bar, which hindered the 

 normal activities of the unfortunate crustacean. 

 'Its comrades came to the rescue, and for one 

 hour's time I watched how they endeavoured to 

 help their fellow-prisoner. They came two at 

 once, pushed their friend from beneath, and after 

 strenuous efforts succeeded in lifting it upright. 

 But then the iron bar prevented them from achiev- 

 ing the work of rescue, and the crab again fell 

 heavily on its back. After many attempts, one of 

 the helpers went into the depth of the tank and 

 brought two other crabs, who began with fresh 

 forces the same pushing and lifting of their help- 

 less comrade. We stayed in the aquarium for 

 more than two hours, and, when leaving, came to 

 cast a glance upon the tank. The work of 

 attempted rescue still continued. Since I saw 

 that I cannot refuse credit to the observation 

 quoted by Dr. Erasmus Darwin that the common 



