624 SCIENCE PROGRESS 



feed, in order that they rnay pursue their meals under cover. 

 The adoption of this very speciaHsed procedure is rendered 

 possible by the secretion, at a much earlier stage of life 

 than is usual in the Order, of the familiar silk which forms 

 so frequent a covering to the pupae of moths. From its 

 earliest days, the Leaf Roller makes use of this material for 

 the purposes of its work. In some cases the leaves are 

 rolled from end to end, in others, two leaves are attached 

 together, while in some the opposite sides are drawn towards 

 each other. In either case, the operation is performed by 

 attaching a line of silk to the two points to be brought into 

 contact and repeatedly shortening them, so that they are 

 drawn together.^ In the most perfect leaf-rolling, the tip of 

 the leaf having been thus drawn up to the standing part, 

 another line is attached to the outside of the roll and this 

 shortened in like manner, the operation being repeated until 

 the whole leaf is rolled up tightly, like a carpet. It is obvious 

 that in this case there are several layers of leaf which can be 

 consumed without the caterpillar exposing itself. Even so, 

 these insects are not entirely safe from enemies. The ends 

 of the roll are open and are not only entered by predatory 

 insects, but even small birds can sometimes extract the occu- 

 pant. These larvae are, therefore, in many cases able to 

 make use of their silk in another manner. Should an enemy 

 enter one end of the roll, the caterpillar attaches a line to the 

 leaf and slips out at the opposite end, falling into midair, 

 where it hangs out of reach of its enemy till the latter has 

 departed. These Tortrix larvae are able to move backward 

 almost as readily as forward. 



V 



It is notable that in this group, in which most species are 

 of indeterminate greyish colour, there is a distinct tendency 

 for green coloration to appear. During a part of its life, as 

 when it is engaged on the construction of its roll, the cater- 

 pillar is exposed, and any tendency to green colouring is bound 

 to assist in hiding it from its vigilant foes. The advance of 

 the race, thenceforward, seems to be more directly connected 

 with the adaptation of colour to environment. The advan- 

 tage of protective coloration is that it affords automatic 

 protection without the necessity for conscious effort on the 

 part of the individual, such as is represented by wood-boring 

 and the construction of a special habitation like these rolls. 

 As protective coloration acts most effectively when there is 



1 It is probably natural shrinkage of the silk, as it dries on exposure, which 

 draws the parts together. 



