330 ANNUAL OF SCIENTIFIC DISCOVERT. 



cies that arc ever tending to dissolve the vital bond, and subjugate the living 

 matter to the ordinary chemical and physical forces. Any changes, there- 

 fore, 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 characterize 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 quad- 

 rupeds, moreover, are more prolific than large ones. Those of the bulk of 

 the mastodons, megatheria, glyptodons, and diprotodons, are uniparotis. 

 The actual presence, therefore, of small species of animals in countries 

 Avhcrc 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 accommodated themselves to changes to which the larger 

 species have succumbed. 



That species should become extinct, appears, from the abundant 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 consid- 

 eration. 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 spe- 

 cies, certainly, probably, or possibly, due to the direct agency of man ; but 

 this cause avails not in the question of the extinction of species at periods 

 prior to any evidence of human existence; it does not help us in the expla- 

 nation of the majority of extinctions, as of the races of aquatic invertebrata 

 and vertcbrata which have successively passed away. 



Within the last century, academicians of St. Petersburg and good natural- 

 ists have described and given figures of the bony and the perishable parts, 

 including the alimentary canal, of a large and peculiar fucivorous Sirenian 

 an amphibious animal like the Manatee, which Cuvier classified with his 

 herbivorous Cetacea, and called Stelleria, after its discoverer. This animal 

 inhabited the Siberian shores and the mouths of the great rivers tl*ere dis- 

 emboguing. It is now believed to be extinct, and this extinction seems not 

 to have been due to any special quest and persecution by man. We may 

 discern in this fact the operation of changes in physical geography, which 

 have, at length, so affected the conditions of existence of the Stelleria as to 

 have caused its extinction. Such changes had operated, at an earlier pei'iod, 

 to the extinction of the Siberian elephant and rhinoceros of the same re- 

 gions and latitudes. A future generation of zoologists may have to record 

 the final disappearance of the Arctic buffalo ( Ovibos moschatus). Fossil re- 

 mains of Ovibos and Stelleria show that they were contemporaries of Elephas 

 primi genius and ^Rhinoceros tfcJtorrhinns. 



The great Auk (Alca impenms, L.) seems to be rapidly verging to extinction. 

 It has not been specially hunted down, like the dodo and dinornis, but by 

 degrees has become more scarce. Some of the geological changes affcctinir 

 circumstances favorable to the well-being of the Alca impennis, have been 



