90 BRITISH LEPIDOPTERA. 



affect caterpillars directly '? Given the origin by hypertrophy of warts 

 and spines, it is then easy to see that by natural selection caterpillars 

 may have finally become adapted so as to mimic similar vegetable 

 growths. Our object is to endeavour to explain the causes of the 

 primary growth and development of such projections, i.e., to lay the 

 foundation for the action of natural selection (Bombycine Moths of 

 America, p. 20). 



With regard to the origin of the humps, by means of which many 

 tree-feeding Geometrid and Notodont larvae resemble portions of their 

 food-plants, Packard further says : The change was probably not 

 necessarily due to the stimulus of the visits and attacks of parasitic 

 insects .... The cause was probably more pervasive, and a result 

 of a change of environment. He considers that they are mere adaptive 

 characters, and may have originated with comparative suddenness, and, 

 in certain families, e.g., the Notodonts, were due to the change from 

 feeding on low plants to an arboreal mode of life. That these had 

 any sudden origin, we do not for a moment believe, and Packard's 

 suggestion that there is a very sudden change in most larvae from a 

 generalised condition in their first and second skins, to a specialised 

 one in the third, is only true so far as there is often a marked change 

 at this stage, but usually the change is a much more gradual one, 

 and only finally culminates in producing the maximum of dense 

 fascicles and hairs towards the end of the caterpillar's existence. 



One of the most remarkable modes of protection adopted by a 

 lepidopterous larva is that of Phorodesma smaragdaria. This larva 

 covers itself with pieces of its food, the particles being bitten off, 

 apparently so that it may the more completely resemble its food-plant. 

 These particles adhere to the skin of the larva by means of a sticky 

 substance, which was generally supposed to come from the mouth, or 

 spinneret, but which White states is excreted by certain glands developed 

 irregularly upon various segments of the body. He says : " These glands 

 are seen, by means of a good lens, to be prominent elongate processes, of 

 an almost pure white colour, each bearing, at the top, a single, rather 

 long, stiff hair, which doubtless serves to spike the fleshy substance of 



the Artemisia The gummy exudation is exceedingly 



tenacious The skin is much wrinkled in the sub- 



spiracular region, forming an irregular and somewhat flattened fringe 

 upon the sides of the anterior segments, adding greatly to the general 

 protective resemblance of the larva to its food-plant " (Proc. Ent. Soc. 

 Loud., 1888, pp. xx-xxi). The larva of the allied P.pustulata is well- 

 known to have a similar habit. 



Apart from the different forms of protective coloration, which larvae 

 assume, and which have been already considered, there are many larvae 

 provided with various conspicuous marks of bright and startling 

 colours, which are supposed to have a terrifying effect on any enemy 

 to whom they are suddenly exposed. Other larvae, again, take up 

 various positions which have been interpreted as being likely to inspire 

 fear in their enemies. Then we find that certain larvae are provided 

 with tubercles which they can move, and the movement of these has 

 also been considered as being of value to their possessor, in aiding in its 

 protection. Others, again, are supposed to be highly coloured as a 

 warning that they are inedible. We can only deal with one or two 

 typical examples to illustrate each of these specialised characters. 



