“Our method is partly founded on the caterpillar, and partly on the perfect insect. We attach the greatest importance to the caterpillar state, and the characters which it furnishes have often more value in our estimation, than those afforded by the butterfly; but generally these characters confirm each other, in other words, two caterpillars presenting the same characters produce flies which likewise partake of the same generic characters. It will no doubt be objected to us, that it is illogical to deduce characters except from the animals we are attempting to classify. We reply, that by following any other plan we must despair of attaining to a natural method. Besides, it is not necessary to be acquainted with the caterpillars of every species; it is sufficient to study a caterpillar and chrysalis of Vanessa or Pieris to have an exact idea of those of the two genera. Even though it should be very difficult to verify the characters taken from the larva, this is no reason why we should abstain from employing them. It is not merely from the fruit that botanists obtain their characters, but likewise from the flower, and even from the first developement of the vegetable embryo. The flower is to the plant what the caterpillar is to the lepidopteron, and the different modes of metamorphosis have as much value as those of inflorescence.
“It appears to us that Latreille’s three divisions, taken from Linnæus—Diurnal, Crepuscular, and Nocturnal—are too inaccurate to be retained, especially the crepuscular section. The denomination Diurnal not only applies to all the known kinds of day butterflies, but also to an almost infinite number of others forming a part of the two other divisions, such as Macroglossa, Zygenides, Castniariæ, Ægocerides, &c. That of Crepuscular is adapted more or less to some sphinges, but by no means to the Zygenides, which fly only in the heat of the sun. Finally, the term Nocturnal is not more properly applicable to all the species, since many belonging to this section appear only during the day. In order to avoid these improper denominations, we have substituted for the word Diurnal, that of Rhopaloceres, proposed by M. Dumeril. Being unable to perceive limits between the Crepuscular and Nocturnal divisions of Latreille, we have united those two great sections under the name of Heteroceres. In our method, therefore, the lepidoptera are divided into two grand legions, Rhopaloceres and Heteroceres[27].”
Dr. Boisduval then proceeds to explain that the first of these divisions is characterised by antennæ thickening to a club at the extremity; and the second, by having these organs variously shaped; this indeed is implied by the words themselves. The first division is subdivided into three sections, according to the manner in which the caterpillars transform themselves into chrysalides. Such as undergo this change by attaching themselves by the tail and a band round the middle, form the first division, named Succincti; such as are suspended by the tail only, the second, Penduli; while those which form a cocoon by rolling leaves together, compose the third division, termed Involuti.
Each of these three sections is then divided into tribes, according to characters derived from the caterpillars and the perfect insect. Among those furnished by the latter, the most important are considered to be the number of ambulatory legs and the form of the palpi. The genera are characterised by the form of the caterpillar and chrysalis, by the dispositions of the nervures of the wings, the form of the antennæ, legs, palpi, thorax, &c. of the perfect insect.
Genus ORNITHOPTERA.
The present generic group was first separated from Papilio by Dr. Boisduval. None of its characters, taken singly, are very strongly marked, but their aggregate importance is sufficiently considerable to authorise its adoption. As in Papilio the antennæ form an elongate club, having the extremity slightly curved upwards, the palpi are longer than in the genus just named, but they never rise above the forehead. The prothorax is much developed anteriorly, and forms a pretty distinct neck. The abdomen is long and robust, that of the male deeply grooved on the under side, and provided at the anal extremity with two large rounded valves. The wings are large, of a strong texture, and furnished with salient nervures; the anterior pair elongate; the posterior with wide shallow indentations, and never prolonged into a tail.
We are very imperfectly acquainted with the natural history of the insects of this group in their early stages. Their remote localities, and the rarity of most of the species, have, for the most part, prevented them from falling under the notice of competent observers. The caterpillar and metamorphoses of one of them (O. Heliacon), however, have been described by Dr. Horsfield. Like the caterpillars of Papilio, it is furnished with two retractile tentacula; the body is large and thick, and bears eight rows of rather long fleshy prominences, of a conical shape. The chrysalis into which it is transformed is somewhat curved, having the head obtuse, and a few projecting points above the middle. It is suspended by the tail, and a transverse band, which, however, does not encompass the body, but is inserted on each side. (See Fig.)
This group is but of limited extent, but it comprehends some of the largest and most beautiful lepidoptera yet known to us. With one exception, which extends over a portion of the Indian continent, they are confined to the Mollucca, Philippine, and others of the numerous and extensive islands of the Indian Archipelago. The species figured, which is the most beautiful of the whole, and to which Linnæus applies the epithet of august, has been long known and highly prized by collectors. It is named