116 president's address SECTION D. 



Asia were the Prototheria. These entered in early Mesozoic 

 or, at all events, pre-cretaceous times, and spread far and 

 wide as is indicated by the wide distribution of their surviving 

 forms. 



Probably also they entered to the north-west rather than 

 to the north-east side, or if on the latter they could not have 

 touched — as Wallace long since pointed out — that portion 

 which was continuous with the northern prolongation of the 

 New Zealand sub-region and along which passed the ancestral 

 struthious birds. 



After a longer or shorter interval, in all probability imme- 

 diately before the cretaceous period and under conditions 

 which enabled them at first to spread with comparative ease 

 over the greater part of the continent, entered the early poly- 

 protodont forms. There is evidence, as will be shown soon, 

 that these also entered towards the north-west rather than 

 towards the north-east. Soon after their entrance the 

 the northern land connection with Asia sank below the sea 

 and though wave after wave of new and higher animal forms 

 reached the southern Asian coast only stragglers crossed at 

 rare intervals to the Island groups between the two conti- 

 nents and fewer still reached Australia. 



At this early period there were thus on the Australian 

 continent two mammalian groups — (1) the Prototheria and 

 (2) the early polyprotodonts — the latter being the representa- 

 tives of the Archi-polyprotodontia. There were no highly 

 specialised marsupial forms and at most only the foreshadow- 

 ings of the main groups. Competition would take place 

 between the Prototherian and Metatherian types resulting in 

 the preservation of only two much modified members of 

 the former, the one protected from marsupial and other 

 foes both by its armour of spines and its burrowing powers ; 

 the other by its amphibious and burrowing habits. Both at 

 and previously to this time Tasmania must have formed a 

 southern prolongation of the continent, and have been easy 

 of access. Gradually the primitive polyprotodonts spread 

 over the whole continent together with the Tasmanian region 

 and gave rise to the various forms now and previously exist- 

 ing ; the one which retained most nearly the primitive form 

 being the Myrmecobius of West and South Australia. It 

 appears, however, as though migration had taken place from 

 the west in a southerly direction and then towards the east, 

 and as if the Cretaceous sea had intervened during this period 

 of migration and prevented ready access to the north-east. 



