GEOMETRIDAE 



413 



greeu or brown, is settled by some determining condition during 

 the first period of larval life and cannot be subsequently modified/ 

 According to Poulton, the dark tint is due in A. betularia to 

 colouring matter in the skin or immediately below it, and the 

 green tint to a layer of fat between the hypodermis and the 

 superficial muscles ; this layer being always green, but more 

 brightly green iu the larvae that are of this colour externally. 

 Much discussion has occurred about these larval attitudes and 

 colours, and it seems probable that Professor Poulton has over- 

 rated the value of protection from birds, mammals and ento- 

 mologists ; the chief destroying agents being other than these, 

 and not liable to be thus deceived, even if the vertebrates are. 

 In some cases such resemblance as undoubtedly exists is not 

 made the best use of. The larva shown in figure 202 bore 

 a wonderful resemblance, when examined, to the rose-twigs it 

 lived on, but the effect of this as a concealing agent was entirely 

 destroyed by the attitude ; for this, being on different lines to 

 those of the plant, attracted the eye at once. This larva, and we 

 may add numerous other larvae, could have been perfectly con- 

 cealed by adopting a different attitude, but never did so ; the 

 position represented being constantly maintained except while 

 feeding. 



In some species of this family the adult females are wdthout 

 wings, or have them so small that they can be of no use for 

 flight. This curious condition occurs in various and widely- 

 separated groups of the Geometridae ; and it would be naturally 

 supposed to have a great effect on the economy of the species 

 exhibiting it, but this is not the case. Some of the flightless 

 females affect the highest trees and, it is believed, ascend to their 

 very summits to oviposit. It has been suggested that they are 

 carried up by the winged males, but this is probably only an 

 exceptional occurrence ; while, as they are known to be capable 

 of ascending with rapidity by means of crawling and running, 

 it may be taken for granted that this is the usual method with 

 them. Some of these wingless females have been found in 

 numbers on gas-lamps, and are believed to have been attracted 

 by the light, as is the case with very many of the winged forms." 



' See Poulton, Tr. ent. Soc. London, 1884, p. 51 ; op. cit. 1892, p. 293 ; and 

 Bateson, p. 213 ; Gould, p. 215. 



^ Giraud, Ann. Soc. ent. France (4), v. 1865, p. 105 ; Fauvel, I.e. Ball. p. liii. 



