Contributions to the Theory of Natural Selection Part 9

g. Helenus-group.

h. Erectheus-group.

i. Pammon-group.

k. Demolion-group.

C. Larvae subcylindrical, variously coloured. Imago with abdominal margin in male plaited, but not reflexed; body weak; antennae short, with a thick curved club; wings entire.

l. Erithonius-group. s.e.xes alike, larva and pupa something like those of P. Demolion.

m. Paradoxa-group. s.e.xes different.

n. Dissimilis-group. s.e.xes alike; larva bright-coloured; pupa straight, cylindric.

D. Larvae elongate, attenuate behind, and often bifid, with lateral and oblique pale stripes, green. Imago with the abdominal margin in male reflexed, woolly or hairy within; a.n.a.l valves small, hairy; antennae short, stout; body stout.

o. Macareus-group. Hind wings entire.

p. Antiphates-group. Hind wings much tailed (swallow-tails).

q. Eurypylus-group. Hind wings elongate or tailed.

Genus LEPTOCIRCUS.

Making, in all, twenty distinct groups of Malayan Papilionidae.

The first section of the genus Papilio (A) comprises insects which, though differing considerably in structure, having much general resemblance. They all have a weak, low flight, frequent the most luxuriant forest-districts, seem to love the shade, and are the objects of mimicry by other Papilios.

Section B consists of weak-bodied, large-winged insects, with an irregular wavering flight, and which, when resting on foliage, often expand the wings, which the species of the other sections rarely or never do. They are the most conspicuous and striking of eastern b.u.t.terflies.

Section C consists of much weaker and slower-flying insects, often resembling in their flight, as well as in their colours, species of Danaidae.

Section D contains the strongest-bodied and most swift-flying of the genus. They love sunlight, and frequent the borders of streams and the edges of puddles, where they gather together in swarms consisting of several species, greedily sucking up the moisture, and, when disturbed, circling round in the air, or flying high and with great strength and rapidity.

_Geographical Distribution._--One hundred and thirty species of Malayan Papilionidae are now known within the district extending from the Malay peninsula, on the north-west, to Woodlark Island, near New Guinea, on the south-east.

The exceeding richness of the Malayan region in these fine insects is seen by comparing the number of species found in the different tropical regions of the earth. From all Africa only 33 species of Papilio are known; but as several are still undescribed in collections, we may raise their number to about 40. In all tropical Asia there are at present described only 65 species, and I have seen in collections but two or three which have not yet been named. In South America, south of Panama, there are 150 species, or about one-seventh more than are yet known from the Malayan region; but the area of the two countries is very different; for while South America (even excluding Patagonia) contains 5,000,000 square miles, a line encircling the whole of the Malayan islands would only include an area of 2,700,000 square miles, of which the land-area would be about 1,000,000 square miles. This superior richness is partly real and partly apparent. The breaking up of a district into small isolated portions, as in an archipelago, seems highly favourable to the segregation and perpetuation of local peculiarities in certain groups; so that a species which on a continent might have a wide range, and whose local forms, if any, would be so connected together that it would be impossible to separate them, may become by isolation reduced to a number of such clearly defined and constant forms that we are obliged to count them as species. From this point of view, therefore, the greater proportionate number of Malayan species may be considered as apparent only. Its true superiority is shown, on the other hand, by the possession of three genera and twenty groups of Papilionidae against a single genus and eight groups in South America, and also by the much greater average size of the Malayan species. In most other families, however, the reverse is the case, the South American Nymphalidae, Satyridae, and Erycinidae far surpa.s.sing those of the East in number, variety, and beauty.

The following list, exhibiting the range and distribution of each group, will enable us to study more easily their internal and external relations.

_Range of the Groups of Malayan Papilionidae._

Ornithoptera.

1. Priamus-group. Moluccas to Woodlark Island 5 species.

2. Pompeus-group. Himalayas to New Guinea, (Celebes, maximum) 11"

3. Brookeana-group. Sumatra and Borneo 1"

Papilio.

4. Nox-group. North India, Java, and Philippines 5 species 5. c.o.o.n-group. North India to Java 2"

6. Polydorus-group. India to New Guinea and Pacific 7"

7. Ulysses-group. Celebes to New Caledonia 4"

8. Peranthus-group. India to Timor and Moluccas (India, maximum) 9"

9. Memnon-group. India to Timor and Moluccas (Java, maximum) 10"

10. Helenus-group. Africa and India to New Guinea 11"

11. Pammon-group. India to Pacific and Australia 9"

12. Erectheus-group. Celebes to Australia 2"

13. Demolion-group. India to Celebes 2"

14. Erithonius-group. Africa, India, Australia 1"

15. Paradoxa-group. India to Java (Borneo, maximum) 5"

16. Dissimilis-group. India to Timor (India, maximum) 2"

17. Macareus-group. India to New Guinea 10"

18. Antiphates-group. Widely distributed 8"

19. Eurypylus-group. India to Australia 15"

Leptocircus.

20. Leptocircus-group. India to Celebes 4"

This Table shows the great affinity of the Malayan with the Indian Papilionidae, only three out of the twenty groups ranging beyond, into Africa, Europe, or America. The limitation of groups to the Indo-Malayan or Austro-Malayan divisions of the archipelago, which is so well marked in the higher animals, is much less conspicuous in insects, but is shown in some degree by the Papilionidae. The following groups are either almost or entirely restricted to one portion of the archipelago:--

_Indo-Malayan Region._ _Austro-Malayan Region._

Nox-group. Priamus-group.

c.o.o.n-group. Ulysses-group.

Macareus-group (nearly). Erechtheus-group.

Paradoxa-group.

Dissimilis-group (nearly).

Brookea.n.u.s-group.

LEPTOCIRCUS (genus).

The remaining groups, which range over the whole archipelago, are, in many cases, insects of very powerful flight, or they frequent open places and the sea-beach, and are thus more likely to get blown from island to island. The fact that three such characteristic groups as those of Priamus, Ulysses, and Erechtheus are strictly limited to the Australian region of the archipelago, while five other groups are with equal strictness confined to the Indian region, is a strong corroboration of that division which has been founded almost entirely on the distribution of Mammalia and Birds.

If the various Malayan islands have undergone recent changes of level, and if any of them have been more closely united within the period of existing species than they are now, we may expect to find indications of such changes in community of species between islands now widely separated; while those islands which have long remained isolated would have had time to acquire peculiar forms by a slow and natural process of modification.

An examination of the relations of the species of the adjacent islands, will thus enable us to correct opinions formed from a mere consideration of their relative positions. For example, looking at a map of the archipelago, it is almost impossible to avoid the idea that Java and Sumatra have been recently united; their present proximity is so great, and they have such an obvious resemblance in their volcanic structure.

Yet there can be little doubt that this opinion is erroneous, and that Sumatra has had a more recent and more intimate connexion with Borneo than it has had with Java. This is strikingly shown by the mammals of these islands--very few of the species of Java and Sumatra being identical, while a considerable number are common to Sumatra and Borneo.

The birds show a somewhat similar relations.h.i.+p; and we shall find that the distribution of the Papilionidae tells exactly the same tale. Thus:--

Sumatra has 21 species } Borneo " 30 " } 20 sp. common to both islands;

Sumatra " 21 " } Java " 28 " } 11 sp. common to both islands;

Borneo " 30 " } Java " 28 " } 20 sp. common to both islands;

showing that both Sumatra and Java have a much closer relations.h.i.+p to Borneo than they have to each other--a most singular and interesting result, when we consider the wide separation of Borneo from them both, and its very different structure. The evidence furnished by a single group of insects would have had but little weight on a point of such magnitude if standing alone; but coming as it does to confirm deductions drawn from whole cla.s.ses of the higher animals, it must be admitted to have considerable value.

We may determine in a similar manner the relations of the different Papuan Islands to New Guinea. Of thirteen species of Papilionidae obtained in the Aru Islands, six were also found in New Guinea, and seven not. Of nine species obtained at Waigiou, six were New Guinea, and three not. The five species found at Mysol were all New Guinea species.

Mysol, therefore, has closer relations to New Guinea than the other islands; and this is corroborated by the distribution of the birds, of which I will only now give one instance. The Paradise Bird found in Mysol is the common New Guinea species, while the Aru Islands and Waigiou have each a species peculiar to themselves.

The large island of Borneo, which contains more species of Papilionidae than any other in the archipelago, has nevertheless only three peculiar to itself; and it is quite possible, and even probable, that one of these may be found in Sumatra or Java. The last-named island has also three species peculiar to it; Sumatra has not one, and the peninsula of Malacca only two. The ident.i.ty of species is even greater than in birds or in most other groups of insects, and points very strongly to a recent connexion of the whole with each other and the continent.