BEHAVIOUR OF SHORE ANIMALS 245 



and placed upon the back by means of the modified last 

 pair of thoracic legs. If the piece of weed is too big and 

 sticks out over the edges of the carapace the crab removes 

 it, cuts a piece off and replaces it. This behaviour, in spite 

 of its apparently intelligent appearance, is said to be of a 

 more or less automatic nature (a statement which those who 

 have witnessed the performance will have difficulty in believ- 

 ing) and to continue unaffected even when the eyes are 

 removed or the brain destroyed (Bohn, op. cit.). Equally 

 interesting is the way in which a crab covered with algse 

 of a particular colour tends to make for the environment 

 which is most in harmony with it, a fact brought out by 

 Aurivilius and later by Mienckewiecz. The nearest we can 

 get to an explanation of these activities at present is to say, 

 with Bohn, that the masking habit of crabs is a complex of 

 activities in which, in addition to differential sensitivity, 

 associative phenomena play a part (see p. 227). 



