344 Studies in the Theory of Descent. 



experimentally. I consider that the ring-spots 

 are crude imitations of the berries of the food- 

 plant. The latter are orange-red, and exactly of 

 the same colour as the spots ; the agreement in 

 colour between the latter and the berries is quite 

 as close as that between the leaves and the 

 general colouring of the caterpillar. I know of 

 no species which more closely resembles the 

 colour of the leaves of its food-plant, the dark 

 upper side and light under side corresponding in 

 the leaves and caterpillars. The colour of the 

 Hippophae is not an ordinary green, but a grey- 

 green, which shade also occurs, although certainly 

 but rarely, in the larvae. I may expressly state that 

 I have repeatedly shown to people as many as six 

 to eight of the large caterpillars on one buckthorn 

 branch, without their being able at once to detect 

 them. It is not therefore mere supposition, but a 

 fact, that this species is protected by its general 

 colouring. At first the orange-red spots appear 

 rather to diminish this protection at least when 

 the insects are placed on young shoots bearing no 

 berries. But since at the same time when the 

 berries become red (end of July and the beginning 

 of August) the caterpillars are in their last stage 

 of development (z. e. possess red-spots), it appears 

 extremely probable that these spots are vague 

 representations of the berries. For the same 

 reason that these caterpillars have acquired the 

 habit of feeding only at dusk and during the 



