292 Studies in the Theory of Descent. 



detect them, even when we are familiar with their 

 habits. 2 



The striking resemblance of many moths to 

 splinters of wood is well known, and to this is 

 added a habit which helps their disguise, viz., that 

 of remaining stiff and motionless on the approach 

 of danger, just like a splinter projecting from the 

 branch. 3 Among the moths coming under this 

 category may be mentioned Cucullia Verbasci, and 

 particularly those of the genus Xylina^ which, when 

 at rest, closely resemble a broken splinter of wood 

 in the colour and marking of their fore wings, and 

 when touched, have a habit of drawing in their 

 legs and falling without opening their wings as 

 though dead. 



That simple adaptive colouring prevails widely 



2 [The adaptive resemblance is considerably enhanced in 

 Catocala and in Lasiocampa Querdfolia by the row of fleshy 

 protuberances along the sides of these caterpillars, which enables 

 them to rest on the tree trunks by day without casting a sharp 

 shadow. The hairs along the sides of the caterpillar of Pacilo- 

 campa Populi doubtless serve the same purpose. (See a paper 

 by Sir John Lubbock, Trans. Ent. Soc. 1878, p. 242; also 

 Peter Cameron, ibid., 1880, p. 75.) It is well known to col- 

 lectors that one of the best methods of finding the caterpillars 

 of the Catocala is to fee! for them by day on the barks of their 

 respective food-trees, or to beat for them at night. R.M.] 



3 [See Wallace's " Contributions to the Theory of Natural 

 Selection," ist ed., p. 62. Also a paper in "Ann. Mag. Nat. 

 Hist." Feb. 1878, p. 159, for cases in point. Rosel in 1746 

 mentioned this habit in Calocampa Exoleta. Hermann Miiller 

 has recorded many other similar instances on the authority of 

 Dr. Speyer ; see " Kosmos," Nov., 1879, p. 114. R.M.] 



