402 TRANSACTIONS OF SECTION D. 
among the Pierines. The structure of these scent-distributors among the 
Lepidoptera is still to a large extent an unexplored field, and their study affords 
a promising subject for further investigation. 
2. Discussion on Mimicry in Australian Insects, introduced by 
Professor EH. B. Pourton, F.R.S. 
It is extremely interesting to compare the phenomena of mimicry as they are 
exhibited in the different parts of the world. We find that the models in each 
tropical region are as a rule related, and often very closely related, to those of 
the other regions. Nevertheless, in spite of these relationships, the models 
commonly exhibit patterns which are peculiar to each region. Thus the 
Danaince and their allies, the tropical American Jthomiine, always tend to be 
mimicked by other butterflies, although their patterns in each of the great 
tropical regions are for the most part very different from those in the others. 
The same conclusions emerge when other great groups of models are compared, 
and the whole body of facts affords strong indirect evidence in support of the 
hypothesis that mimicry is an advantageous resemblance which has grown up 
under the influence of natural selection. 
Australia is the most isolated of all the inhabited continental tracts on the 
earth’s surface, and its isolation is reflected in its peculiar fauna and flora. How 
far is it reflected in the insect-models and their mimics? Up to the present 
time the subject has been but little studied in Australian material, but we can 
nevertheless see our way to certain conclusions of much interest. 
Perhaps the most widely spread models in the world are the black yellow- 
banded stinging Hymenoptera. The central members of these powerful com- 
binations are wasps (Diploptera), around which are ranged sand-wasps (Fossores), 
and, in far smaller numbers, bees (Anthophila), followed by mimetic species 
of the Phytophagous Hymenoptera, and of other orders—Diptera, Coleoptera, 
Lepidoptera, ete. Throughout this dominant combination of models and mimics 
the subcylindrical body is black, encircled by many bright yellow bands. 
Although widespread over the world it is especially powerful in the north 
temperate zone. In Australia, however, its place is taken by a combination 
with a very distinct pattern. The bands are deep brownish orange instead of 
bright yellow, and they are few and broad instead of many and narrow. This 
pattern runs through a large and complex set of models and mimics. It is very 
convincing to compare such a mimetic Asilid fly as the European Asilus 
crabroniformis with the Australian species, and to observe how their very 
different patterns resemble those of the respective Aculeate models. An equally 
significant comparison may be drawn between the mimetic Longicorn beetles of 
these two parts of the world. 
The conspicuous sluggish Lycid beetles form another dominant group of 
models in all the tropical regions, and here, too, a powerful Australian com- 
bination exhibits a peculiar colouring, and in some respects a peculiar 
constitution. 
Material already received from Commander J. J. Walker in the Sydney 
district and from Mr. A. Eland Shaw at Healesville, Victoria, shows that the 
Australian contribution to the study of mimicry is sure to be of the highest 
interest and importance. 
TUESDAY, AUGUST 18. 
Joint Discussion with Section K on the Nature and Origin of Species. 
See p. 579. 
The following Papers were then read :— 
1. An Expedition to the Abrolhos Islands. By Professor W. J, Daxry, 
