Fig. 153.—Cyphocrania aestuans; individual in which the right front leg has been renewed. Senegal. (After Westwood.)
We have pointed out that the tegmina or upper wings are usually of small size or absent (Fig. 150, Aschipasma catadromus), even in the species where the lower wings are very largely developed; in such cases the latter organs are folded in a complicated, fan-like manner, and repose on the back, looking as if they were really the tegmina (Fig. 159, Calvisia atrosignata); this appearance, moreover, is in some species enhanced much by the fact that the part of the wing which is outermost in the folded state is quite differently coloured from the rest of the organ. The colour of the body in many Phasmidae is said to be very variable, and if the tints be owing to chlorophyll or other plant juices, finding their way amongst the Insect-tissues, this is readily understood; in Diapheromera the young Insect is brownish on hatching, becomes green after feeding, and turns brown again when the leaves do so. The ocelli, too, are said to be very variable, and M‘Coy goes so far as to state[[194]] that they may be either present or absent in different individuals though of the same species and sex,—a statement so remarkable as to require minute examination, though it is to some extent confirmed by the remarks of other entomologists.
Fig. 154.—Phyllium scythe, female. Sylhet. (After Westwood.)
The resemblance presented by different kinds of Orthoptera to leaves is so remarkable that it has attracted attention even in countries where Natural History is almost totally neglected; in many such places the inhabitants are firmly convinced that the Insects are truly transformed leaves, by which they understand a bud developing into a leaf and subsequently becoming a walking-leaf or Insect. To them the change is a kind of metamorphosis of habit; it grew as a leaf and then took to walking.[[195]] It is usually the tegmina that display this great resemblance to vegetable structures, and there is perhaps no case in which the phenomenon is more marked than it is in the genus Phyllium, the members of which occur only in the tropical regions of the Old World, where they extend from Mauritius and the Seychelles to the Fiji Islands—possibly even more to the East—and have, it would appear, a peculiar penchant for insular life.
Fig. 155.—Phyllium scythe, male. Sylhet. (After Murray.)
The genus Phyllium constitutes by itself the tribe Phylliides. Although the characters and affinities of this group have been only very inadequately investigated, it will probably prove to be a very distinct and isolated one. The species are not well known, but are probably numerous, and the individuals are believed not to be rare, though the collections of entomologists are very badly supplied with them. The resemblance of the tegmina or front wings to leaves is certainly of the most remarkable nature. During the early life the Insect does not possess the tegmina, but it is said then to adapt itself to the appearance of the leaves it lives on, by the positions it assumes and the movements[[196]] it makes. When freshly hatched it is of a reddish-yellow colour. The colour varies at different periods of the life, but "always more or less resembles a leaf." After the young Insect has commenced eating the leaves it speedily becomes bright green; and when the metamorphosis is completed the female Insect is possessed of the leaf-like tegmina shown in Figs. 154, 156. Before its death the specimen described by Murray passed "through the different hues of a decaying leaf." Brongniart has had opportunities of observing one of these leaf-Insects, and has, with the aid of M. Becquerel, submitted their colouring matter to spectral analysis,[[197]] with the result of finding that the spectrum exhibits slight distinctions from that of solutions of chlorophyll, but does not differ from that of living leaves. Mr. J. J. Lister when in the Seychelles brought away living specimens of Phyllium; and these becoming short of food, nibbled pieces out of one another just as they might have done out of leaves. The Phasmidae are purely vegetable feeders, and these specimens did not seriously injure one another, but confined their depredations to the leaf-like appendages and expansions.
The males of this genus are totally different from the females; the foliaceous tegmina being replaced by appendages that are not leaf-like, while the posterior wings, which are large and conspicuous parts of the body, have no leaf-like appearance (Fig. 155).
