204 THE COLOUES OF ANIMALS 



the smell alone is generally sufficient to repel them. 

 Many Crustacea are known to live in the canal systems 

 of sponges, and are thus protected. The significance 

 of this association is to be found in the fact that 

 Crustacea are the animals most relished and sought 

 after by fishes, and that sponges are extremely re- 

 pugnant to the latter. 



Such cases as these are some indication of the 

 severity of the struggle for existence among marine 

 forms of life. Very interesting evidence of this is to 

 be found in Bateson's notes on the protective habits 

 of shrimps and prawns. 1 He states that the wrasse 

 will find a shrimp if the least bit be exposed, in spite 

 of its protective colouration. If, however, ' the sand be 

 fine, a shrimp will bury itself absolutely.' We can 

 well understand the immense advantage which would 

 be gained by a much persecuted crustacean if it 

 associated with some animal repugnant to its foes. 



Colours and markings which direct the attention of an 

 enemy to some non-vital part, but which are not 

 attended by unpleasant qualities 



From cases such as those which have been just 

 described we pass, by a very natural transition, to 

 colours and markings which attract the attention 

 of an enemy to some non-vital part after the animal 



1 Journ. Mar. Biol. Ass., New Series, vol. i. no. 2, Oct. 1889, pp. 

 211 et seq. 



