DARWIN 5 



offer them all the kinds they can obtain, and carefully note 

 (i) which they eat, (2) which they refuse to touch, and (3) 

 which they seize but reject. If the name of the caterpillar 

 cannot be ascertained, a short description of its more promi- 

 nent characters will do very well, such as whether it is hairy 

 or smooth, and what are its chief colours, especially distinguish- 

 ing such as are green or brown from such as are of bright 

 and conspicuous colours, as yellow, red, or black. The food 

 plant of the caterpillar should also be stated when known. 

 Those who do not keep birds, but have a garden much fre- 

 quented by birds, may put all the caterpillars they can find 

 in a soup plate or other vessel, which must be placed in a larger 

 vessel of water, so that the creatures cannot escape, and then 

 after a few hours note which have been taken and which left. 

 If the vessel could be placed where it might be watched from 

 a window, so that the kind of birds which took them could 

 also be noted, the experiment would be still more complete. 

 A third set of observations might be made on young fowls, 

 turkeys, guinea-fowls, pheasants, etc., in exactly the same 

 manner. 



" Now the purport of these observations is to ascertain the 

 law which had determined the coloration of caterpillars. The 

 analogy of many other insects leads us to believe that all those 

 which are green or brown, or of such speckled or mottled 

 tints as to resemble closely the leaf or bark of the plant on 

 which they feed, or the substance on which they usually repose, 

 are thus to some degree protected from the attacks of birds 

 and other enemies. We should expect, therefore, that all 

 which are thus protected would be greedily eaten by birds 

 whenever they can find them. But there are other caterpillars 

 which seem coloured on purpose to be conspicuous, and it is 

 very important to know whether they have another kind of 

 protection, altogether independent of disguise, such as a dis- 

 agreeable odour and taste. If they are thus protected, so that 

 the majority of birds will never eat them, we can understand 

 that to get the full benefit of this protection they should be 

 easily recognized, should have some outward character by 

 which birds would soon learn to know them and thus let them 



