PROTECTIVE EESEMBLANCES IN LEPIDOPTERA 35 



thick branches. They lie flattened and closely pressed 

 against the bark ; while the furrow which would lead 

 to their detection is partially filled up, and the 

 shadow neutralised, by a row of fleshy protuberances 

 in the caterpillars of the Bed and Crimson Under- 

 wing Moths {Catocalidce ; see figs. 38 and 39, page 

 151), and by hairs in the larva of the December Moth 

 {Poecilocampa populi). This interpretation was first 

 offered by Meldola, and it is strongly supported by 

 the previously mentioned fact that similar protuber- 

 ances occur in Geometrce, and are strictly confined to 

 the comparatively short line of contact between the 

 larva and the branch. The lichens on the bark are 

 very commonly resembled rather than the bark itself. 

 This is the case with the last-named larva. The 

 caterpillar, chrysalis, and moth of the Black Arches 

 {Psilura monacha) are beautifully protected in this 

 way. The black pupa is fixed in a chink in the bark 

 by a few inconspicuous threads ; its dark colour har- 

 monises with the shadow in the chink, while the long 

 tufts of greyish hair project and exactly resemble the 

 appearance of lichen. Both larva and moth are 

 coloured so as to resemble common appearances pre- 

 sented by lichens, and both habitually rest on lichen- 

 covered bark. A lichen-feeding Geometer {Cleora 

 lichenaria) is wonderfully protected in the same 

 manner; the larva often twists itself among the 

 irregularities of the lichen, so that it is completely 



