110 Professor Owen, [April 12, 



existing analogues. To match the eocene palaeotheres and lophiodons 

 we must bring tapirs from Sumatra or South America; and we must 

 travel to the antipodes for myrmecobians, the nearest living analogue 

 to the amphitheres and spalacotheres of our oolitic strata. 



On the problem of the extinction of species I have little to say ; 

 and of the more mysterious subject of their coming into being, nothing 

 profitable or to the purpose, at present. As a cause of extinction in times 

 anterior to man, it is most reasonable to assign the chief weight to those 

 gradual changes in the conditions affecting a due supply of sustenance 

 to animals in a state of nature which must have accompanied the 

 slow alternations of land and sea brought about in the aeons of geo- 

 logical time. Yet this reasoning is applicable only to land animals ; for 

 it is scarcely conceivable that such operations can have affected sea- 

 fishes. 



There are characters in land-animals rendering them more obnoxious 

 to extirpating influences, which may explain why so many of the larger 

 species of particular groups have become extinct, whilst smaller 

 species of equal antiquity have survived. In proportion to its bulk is 

 the difficulty of the contest which the animal 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 forces. Any changes, therefore, in such external agencies as 

 a species may have been originally adapted to exist in, will militate 

 against that existence in a degree proportionate to the size which may 

 characterise the species. If a dry season be gradually prolonged, the large 

 mammal will suffer from the drought sooner than the small one ; if such 

 alteration of climate affect the quantity of vegetable food, the bulky 

 herbivore will first feel the effects of stinted nourishment ; if new 

 enemies be introduced, the large and conspicuous animal will fall a 

 prey while the smaller kinds conceal themselves and escape. Small 

 quadrupeds, moreover, are more prolific than large ones. Those of 

 the bulk of the mastodons, megatheria, glyptodons, and diprotodons, 

 are uniparous. 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 degeneration — 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 and accommo- 

 dated themselves to changes to which the larger species have suc- 

 cumbed. 



That species should become extinct appears, from the abundant 

 evidence of the fact of extinction, to be a law of their existence ; 

 whether, however, it be inherent in their own nature, or be relative 

 and dependent on inevitable changes in the conditions and theatre of 

 their existence, is the main subject for consideration. But, admitting 

 extinction as a natural law which has operated from the beginning of 

 life on this planet, it might be expected that some evidence of it should 

 occur in our own time, or within the historical period. Reference has been 

 made to several instances of the extirpation of species, certainly, pro- 



