ii.] PROBABLE CAUSE OF THE CHANGES. 57 



willow and sallow ; S. populi, which feeds on the 

 poplar ; and S. tilice, which frequents the lime, the 

 caterpillars all remain green ; while in those which 

 frequent low plants, such as the convolvulus hawk- 

 moth, which frequents the convolvulus ; Chcerocampa 

 nerii, which feeds in this country on the periwinkle ; 

 Chcerocampa celerio, Ch. elpenor, and Ch. porcellus, 

 which live on galium, most of the caterpillars turn 

 brown. There are, indeed, some caterpillars which are 

 brown, and still do not go down to the ground, as, for 

 instance, those of Aspilatis aspersama, and indeed of 

 the GfeometridcB generally. These caterpillars, however, 

 as already mentioned, place themselves in peculiar 

 attitudes, which, combined with their brown color, 

 make them look almost exactly like bits of stick or 

 dead twigs. 



The last of the five points to which I called your 

 attention was the eye-spots. In some cases, spots may 

 serve for concealment, by resembling the marks on 

 dead leaves. In Deilephila hippopkae, which feeds 

 on the hippophae, or sea buckthorn, a grey-green 

 plant, the caterpillar also is a similar grey-green, and 

 has, when full grown, a single red spot on each side, 

 which, as Weissmann suggests, at first sight much 

 resembles in color and size one of the berries of 

 hippophae. This might, at first, be supposed to 

 constitute a danger, and therefore to be a disadvan- 

 tage, but the seeds, though present, are not ripe, and 

 consequently are not touched by birds. Again, in 

 Chcerocampa tersa, there is an eye-spot on each segment, 

 which mimics the flower of the plant on which it feeds 

 (Spermacoce hyssopifolia). White spots, in some cases, 



