The differences of form are equally clear. _Papilio Pammon_ everywhere on the continent is tailed in both sexes. In Java, Sumatra, and Borneo, the closely allied _P. Theseus_ has a very short tail, or tooth only, in the male, while in the females the tail is retained. Further east, in Celebes and the South Moluccas, the hardly separable _P. Alphenor_ has quite lost the tail in the male, while the female retains it, but in a narrower and less spatulate form. A little further, in Gilolo, _P. Nicanor_ has completely lost the tail in both sexes. _Papilio Agamemnon_ exhibits a somewhat similar series of changes. In India it is always tailed; in the greater part of the archipelago it has a very short tail; while far east, in New Guinea and the adjacent islands, the tail has almost entirely disappeared. In the _Polydorus_-group two species, _P. Antiphus_ and _P. Diphilus_, inhabiting India and the Indian region, are tailed, while the two which take their place in the Moluccas, New Guinea, and Australia, _P. Polydorus_ and _P. Leodamas_, are destitute of tail, the species furthest east having lost this ornament the most completely. Western species, tailed. Eastern species (closely allied), less tailed. Papilio Pammon (India) tailed. P. Thesus (islands) very short tail. P. Agamemnon, var. tailed. P. Agamemnon, var. not tailed. (India) (islands) P. Antiphus (India, tailed. P. Polydorus (Moluccas) not tailed. Java) P. Diphilus (India, tailed. P. Leodamas (New not tailed. Java) Guinea) The most conspicuous instance of local modification of form, however, is exhibited in the island of Celebes, which in this respect, as in some others, stands alone and isolated in the whole archipelago. Almost every species of _Papilio_ inhabiting Celebes has the wings of a peculiar shape, which distinguishes them at a glance from the allied species of every other island. This peculiarity consists, first, in the upper wings being generally more elongate and falcate; and secondly, in the costa or anterior margin being much more curved, and in most instances exhibiting near the base an abrupt bend or elbow, which in some species is very conspicuous. This peculiarity is visible, not only when the Celebesian species are compared with their small-sized allies of Java and Borneo, but also, and in an almost equal degree, when the large forms of Amboyna and the Moluccas are the objects of comparison, showing that this is quite a distinct phenomenon from the difference of size which has just been pointed out. In the following Table I have arranged the chief Papilios of Celebes in the order in which they exhibit this characteristic form most prominently. (See Plate VIII.)