THE COLORATION PROBLEM. 97 



colonies of unicellular organisms on the outside of the ants, but as she 

 is still working at the matter, it is perhaps best to leave it here, till 

 more definite results have been obtained. 



The Coloration Problem. 



By W. PARKINSON CURTIS, F.E.S. 

 {Continued front page 61.) 



So much for the methods of the birds. Now as to the optical 

 capacity of birds, I find that generally it seems to me to be much the 

 same as my own (possibly exactly the same as my own), but where I 

 think the bird's sight differs from mine lies, not so much in what their 

 eyes perceive, as in what the perception conveys to their brain. What 

 do they deduce from what they see, or what response does their organi- 

 sation give to the stimuli received through their optic centres ? 

 Ex liyjiotlied, unless the sight of the insect moving or at rest be coupled 

 with the power to deduce, or the response to the stimulus, that there 

 goes a palatable meal or an unpalatable one, well, the insect might as 

 well not be seen, for both Batesian and Miillerian theories require 

 attacks {Confer, Cockayne, Proc. Eat. Sue. Land., 1911, p. 168). 



My own experience confirms the recorded observations of many 

 other observers, the moving insect is attacked where the still one often 

 escapes. I have noticed this particularly with larvte of cryptic 

 coloi'ation, and I can call to memory one particular instance. I was 

 watching a green caterpillar on a green leaf in my conservatory 

 (I knew the caterpillar, probably a small green rhloi/ophora meticnlo.m, 

 was there, I had previously seen it), I was also watching Erithaca 

 rubecula (the Robin), which Avith characteristic impudence makes a 

 practice of hunting for food in the conservatory, spending all night 

 there quite happily. I wondered exactly how long it would be before the 

 Eobin would find the caterpillar. The problem was soon solved, the 

 caterpillar made a slight (very slight) movement, and the Robin, then 

 several feet distant, hustled across and demolished it promptly. I 

 think that the golden rule with all cryptically coloured animals, and 

 one that they seem to follow with almost unvarying regularity, is, 

 when in presence of danger " freeze," when in doubt " freeze," except 

 when absolutely necessary to move, don't move. Instances of 

 '' freezing " habit are perhaps unnecessary, as it is well known, but 

 last Spring on two occasions I surprised Roebuck. I regard Roebuck 

 (Capreoliis capraea. Gray) as a cryptically coloured animal. The 

 Roebuck, one on the open heath, and one amongst sparse bushes on a 

 heathy brake in a wood, " froze," so did I ; on one occasion I stared 

 the Roebuck out, on the other the Roebuck stared me out, but until 

 the animal lost its nerve it never moved a hair and looked for all the 

 world like a dead weather beaten oak stump. Lt.-Col. Manders also 

 agrees that want of movement tends to invisibility. I have heard 

 still elephants likened to termite's nests. On the other hand, when 

 the insect does move, it is instantly attacked. This fact points to the 

 conclusion that the bird recognises the moving butterfly or moth as a 

 palatable meal, or why should the bird trouble to perform the com- 

 plicated evolutions necessary to enable it to catch the msect. That 

 quick recognition confirms that the bird has tested and found good 



