X 



the difficulty of the contest which, as a living organized whole, the individual of such 

 species has to maintain against the surrounding agencies that are ever tending to 

 dissolve the vital bond, and subjugate the living matter to the ordinary chemical and 

 physical Ibices. Any changes, therefore, in such external conditions as a species may 

 have been originally adapted to exist in, will militate against that existence in a degree 

 proportionate, perhaps in a geometrical ratio, to the bulk of the species. If a dry 

 season be gradually prolonged, the large Mammal will suffer from the drought sooner 

 than the small one; if any alteration of climate affect the quantity of vegetable food, 

 the bulky Herbivore will first feel the effects of stinted nourishment. 



" The actual presence, therefore, of small species of animals in countries where larger 

 species of the same natural families formerly existed, is not the consequence of any 

 gradual diminution of the size of such species, but is the result of circumstances which 

 may be illustrated by the fable of the ' oak and the reed ;' the smaller and feebler animals 

 have bent, as it were, and accommodated themselves to changes which have destroyed 

 the larger species"*. 



To the surmise that, through geological and climatal changes, a gradual reduction 

 of the source's of nutriment had been associated, as the cause, with the diminished size 

 of existing vegetarian Marsupials, it might be remarked that it is hard to believe that 

 Diprotodonts, Xototheres, Procoptodonts, and Phascolones could not find subsistence 

 where the herds of cattle and horses now " increase and multiply." And if, in Australia, 

 the course of extirpation dated from the incoming of man with his canine satellite, the 

 smaller kinds of aboriginal Marsupials may have added to the advantage in escape and 

 concealment due to such character the gradually acquired habit of browsing by moonlight 

 and at dawn and dusk rather than in the glare of day. 



The sources to which I have been indebted for the fossils described and figured in the 

 present work are duly acknowledged in each instance ; the name of my early fellow- 

 labourer and friend George Bennett, M.D., F.L.S., will be found in almost every 

 Section; and it only remains for me to express grateful thanks for the liberal votes 

 of the Legislatures of New South Wales and South Australia, and the generous aid 

 of Sir George Macleay, K.C.M.G., through which, mainly, I have been enabled to issue 

 the volume in its present form and with its numerous plates and woodcuts. 



• See ' Transactions of the Zoological Society of London,' torn. cit. p. 14, and the further development of the 

 principle of the " contest for existence," or "hattle of life,'' in Darwin ' On the Origin of Species,' 12mo, 1859. 

 Evidence, however, of the influence of this dynamic, beyond the extinction of species, has not yet reached me. 



