Tlie Colours of Animals. 87 



and would make the creature more conspicuous 

 When, therefore, the diagonal lines are developed, 

 the longitudinal ones often disappear. There is 

 one other point in connection with these diagonal 

 lines to which I must call your attention. 



4. In many species they are white, but in some 

 cases as, for instance, in the beautiful green cater- 

 pillar of the Privet Hawk-moth the white streak 

 is accompanied by a coloured one, in that case lilac. 

 At first we might think that this would be a dis- 

 advantage, as tending to make the caterpillar more 

 conspicuous ; and in fact, if we put one in full view 

 for instance, out on a table and focus the eye 

 on it, the coloured lines are very striking. But we 

 must remember that the habit of the insect is to sit 

 on the lower side of -the leaf, generally near the 

 middle rib, and in the subdued light of such a 

 situation, especially if the eye be not looking 

 exactly at them, the coloured lines beautifully 

 simulate a line of soft shadow, such as must always 

 accompany a strong rib ; and I need not tell any 

 artist that the shadows of yellowish-green must be 

 purplish. Moreover, any one who has ever found 

 one of these large caterpillars will, I am sure, agree 

 with me that it is surprising, when we consider 

 their size and conspicuous colouring, how difficult 

 it is to see them. 



5. But though the prevailing colour of caterpillars 

 is green, there are numerous exceptions. In one 

 great family of moths the prevailing colour is brown. 



