New Discoveries Concerning the Octopus. 25 



sia particularly, interested him. He found it feeding 

 on the sea-weed, and when disturbed it emitted the 

 peculiar purple fluid for which it is noted. The 

 pools of water left by the outgoing tide formed 

 aquaria of more than ordinary interest. The octo- 

 pus was the subject of many observations, numbers 

 of which were seen clinging to the rocks by their 

 eight sucker-lined arms, or dashing across the pool, 

 ejecting the cloud of ink which constitutes a part of 

 their defence. 



The young naturalist was quick to note their 

 power of mimicry, a fact in this and other animals 

 that was dwelt upon in later years by himself and 

 Wallace. He noticed that they changed their tints 

 according to the ground over which they passed, 

 and a close examination showed that clouds of colour 

 were continually passing over them, varying from 

 hyacinth-red to chestnut-brown in tint. 



Darwin was probably the first to apply a galvanic 

 battery to these beautiful creatures, with the result 

 that the part touched became almost black. He 

 noticed that they changed colour under all circum- 

 stances, whether swimming or resting, and was the 

 first to call attention to the fact that the ink was 

 used as a means of concealing the direction of re- 

 treat. One cuttle-fish in this natural aquarium 

 ejected water above the surface from a hole in 

 which it lay concealed, and he suspected that it 

 could direct its aim by turning its tube or siphon in 

 a given direction. Whether this is true or not 

 would be difficult to ascertain, but the author has 

 seen a squid force its stream of ink a foot or more 



