50 BRITISH LEPIDOPTEKA. 



examined carefully at each ecdysis. The case of Aglais urticae and 

 others occur to me. 



The horn which characterises the Sphingid caterpillars is, as we 

 have seen, placed on the dorsum of the eighth abdominal segment, and 

 it is remarkable that when it is absent in allied forms, it is replaced by 

 a small, low and flattened tubercle, the segment itself being somewhat 

 swollen. Many Noctuid larva? — Amphipyra, Mamestra persicariae, etc., 

 have a prominent hump on this segment, so also have the larvae of 

 the Agaristidae, and others. In many Notodont larva? the first ab- 

 dominal segment bears a conspicuous hump, sometimes forked, often 

 ending in a seta. It would appear, from Packard's researches, that 

 the three thoracic segments, and the first and eighth abdominal seg- 

 ments, are those most usually characterised by tall fleshy tubercles, 

 horns, etc. The same author shows that the first and eighth ab- 

 dominal segments bear no prolegs, and that, when walking, these 

 apodous segments are more raised than the others, and that, if it be 

 true, as it appears to be, that these humps do frequently rise from 

 the most elevated portions of the larva when crawling, then the move- 

 ment of these conspicuous structures might tend to be of service in 

 frightening away other creatures. He further suggests that the 

 humping or looping of these segments may have had something to do 

 with inducing the hypertrophy of the dermal tissues which enter 

 into the formation of the tubercles or horns, whilst with regard to the 

 mutant or movable tubercles, he suggests that the movement of these 

 appendages would suffice to scare off an approaching ichneumon or 

 Tachina. 



Larvse are, of course, subject to the conditions involved by the 

 struggle for existence, and to modification in relation to environment, 

 and, hence, is due the modification of the setiferous tubercles, by 

 which the larva is made to resemble different objects at different phases 

 of its existence. Everyone knows how different is the larva of Jocheaera 

 alni® in its third skin, in what is known as the " birds'-dropping " 

 stage, from the adult larva with its conspicuous bulbous-tipped 

 hairs. This reference to a subject already discussed in a previous 

 part of this chapter (p. 47) gives us a chance of explaining why 

 we have thrown doubt upon Dyar's statement that " we do not 

 find intergrading forms between the single-haired tubercle and the 

 many-haired wart." He probably had in mind some such change as 

 that occurring in the Anthrocerids, in which the simple single-haired 

 tubercle of the first skin becomes a many-haired wart in the second, 

 increasing in size at each subsequent moult. It happens, as a matter 

 of fact, that intergrading forms are exceedingly common in many 

 species of Lepidoptera, a single-haired tubercle in the first skin ac- 

 quiring some hairs at each subsequent moult, until it becomes a wart. 

 In the Acronyctid larvse there are various stages in different species, 

 even in the first skin, the differences extending from a one-haired 

 tubercle, two-haired tubercle, etc., to a many-haired wart, and such 

 cases are not at all uncommon. In the case of Anthrocera, it is pos- 

 sible that some stages in the evolution of the many-haired wart are 

 now missed, but, in others, the intergrading forms are, as we have 

 said, by no means unknown. 



* Chapman, Entomologist's Record, etc., vol. ii., p. 123, 



