108 THE VALUE OF COLOUR 



to the fronds of the sea-weed both in shape and in color. 

 The concealment of the animal may be judged from the fact 

 that we found the animal quite by accident on a piece of 

 Sargassum that had been in a glass jar in the laboratory for 

 some time, and had been closely examined in the search for 

 hydroids and the like without disclosing the presence upon 

 it of two large specimens of the Scyllaea (the animal, as 

 I recall it, is about two inches long). It was first detected 

 by its movements alone, by someone (I think a casual visitor 

 to the laboratory) who was looking closely at the Sargassum 

 and exclaimed, " Why, the sea-weed is moving its leaves ! " 

 We found the example in the summer of 1880 or 1881 at 

 Beaufort, N.O., where the Johns Hopkins laboratory was 

 located for the time being. It must have been seen by many 

 others, before or since. 



' I wrote and sent to Darwin a short description of the 

 case at the suggestion of Brooks, with whom I was at the 

 time a student. I was, of course, entirely unknown to 

 Darwin (or to anyone else) and to me the principal interest 

 of Darwin's letter is the evidence that it gives of his extra- 

 ordinary kindness and friendliness towards an obscure 

 youngster who had of course absolutely no claim upon his 

 time or attention. The little incident made an indelible 

 impression upon my memory and taught me a lesson that 

 was worth learning.' 



VARIABLE PEOTECTIVE RESEMBLANCE 



The wonderful power of rapid colour adjust- 

 ment possessed by the cuttle-fish was observed 

 by Darwin in 1832 at St. Jago, Cape de Verd 

 Islands, the first place visited during the voyage 

 of the Beagle. From Eio he wrote to Henslow, 

 giving the following account of his observations, 

 May 18, 1832 :— 



' I took several specimens of an Octopus which possessed 

 a most marvellous power of changing its colours, equalling 



