9 
in southeast x\sia, Malay archipelao-o. New Guinea, north 
Australia ami the Solomons. They show considerable ^eo- 
pjrapliical variation and many subspecies are recog’nised. 
He assumed that the "‘roup had evolved in phyloo-enetie 
stages, the most recent being Stage Z. At the l)eginning 
of Stage Z each of the present day species had one form 
only and had not differentiated into subspecies. He 
grouped the most closely related species together and con- 
sidered that the species of each group had evolved as 
subspecies during Stage Y from one earlier species. In all 
he traced back six phylogenetic stages to the common ances- 
tor of the four genera, and at the same time considered 
the probable centres of dispersal of the groups at each 
stage. After that Zeuner turned to the geological history 
of the region for an explanation of the degree o'" relation- 
ship of the various groups and of their present distribution. 
Stage Z in which the geographical subspecies have 
formed is regai'ded as the recent post-glacial era of 10,000- 
20,000 years; stage Y in whicli the species were formed as 
the Pleistocene ])eriod or h'e Age of 500 000-1,000,000 yrs. 
During the Pleistocene periods of glaciation the sea level 
was 50-100 fathoms lower than today, while at periods 
when the ice melted it may have been 50 fathoms higlier. 
This meant periods when migration was possible, followed 
by periods of isolation and will account satisfactorily for 
the dispersal of the butterflies dindng the Z and Y stages. 
Correlating the earlier stages with the geological his- 
tory is more complicated. The more primitive species 
groups of Orniihopfera occur in the Moluccas and Solomon 
Jsla)ids and appear to have by-passed New Guinea. This 
odd distribution can be explained by the theory o^*' contin- 
ental drift, according to which the Australian block has 
been d]‘ifting northwai'd since the eaidy Tertiaiw and New 
Guinea has been pushed in amongst the northern island 
chains. If New Guinea were withdrawn to the southeast 
and the island chains straightened out, it would bring the 
Moluccas sufficiently near to the Solomons to account for 
the early Ornifhoptera reaching them. 
On the other hand according to another entomologist, 
L. E. Cheesman, New Guinea was at that time connected 
by a land mass to Asia, and there are ancient rocks along 
the north coast of New Guinea and in New Britain, some of 
which have never been submerged. 
Whoever is right, you can see that the taxonomist 
who wants to understand the present distribution of the 
group he is interested in, may have to study geological 
facts and theories. At the same time, geologists can use 
the evidence provided by taxonomists to test their theories 
