VAEIABLE PEOTECTIVE RESEMBLANCE IN INSECTS 157 



are witnessing the results of a power of adjustment 

 which existed in the past but is now lost. I think, on 

 the other hand, that variability or dimorphism pre- 

 ceded the power of adjustment in all cases. I have 

 already shown that these appearances possess a pro- 

 tective value even when they cannot be adjusted (see 

 pp. 46-4.8) . When Variable Protective Eesemblance is 

 present, but acts somewhat uncertainly (as in the larva 

 of the Eyed Hawk Moth), it is probable that the power . 

 has been only recently acquired and is still imper- 

 fect. This conclusion is supported by the fact that 

 the closely allied caterpillar of the Convolvulus Hawk 

 Moth {Sphinx convolvuli) has no power of adjustment, 

 although it is completely dimorphic ^ (see pp. 47, 48). 

 Before finally leaving this part of the subject I 

 will briefly allude to facts which render it probable that 

 certain perfect insects possess the power of Variable 

 Protective Eesemblance. 



Variable Protective Resemblance probable in certain 

 Moths 



The colour of certain insects varies with the pre- 

 vailing tint of the locality in which they occur. The 

 best instance known to me is that of one of the 

 Geometrce, the Annulet Moth (Gnophos obscurata). 

 This moth is light-coloured in chalky localities (e.g. 

 on the chalk at Lulworth), but darker when the pre- 



' Trans. Ent. Soc. Lond. 1888, pp. 552-653. 



