356 ANOTHER STATISTICAL QUERY. 



simultaneously. Our animal, which a small lens makes very 

 distinct, has been more than once confounded with the Sarcoptes 

 scabieL 



Let us resume. Our cheese-dust, which to all appearance 

 walks alone, encloses legions of mites ; the old you may detect 

 by their eight feet, the young by having six. The germs, or 

 eggs, whence they spring, are found mixed among the excre- 

 ments of the living, and the ddbris of the dead. 



It is in this way that a crust of cheese offers us a true, a 

 vivid image of the terrestrial crust. So may we learn to com- 

 pare small things with great. 



How MANY ANIMAL SPECIES ARE THERE DISTRIBUTED OVER 

 THE SURFACE OF THE GLOBE? 



In the present condition of scientific knowledge, no satis- 

 factory answer can be given to this important and most 

 interesting question. 



The truth is, that what we may call Geographical Zoology 

 is as yet in its very infancy. The few works which have been 

 published on the subject have been published within the last 

 eighty or ninety years ; and they embrace only the vertebrate 

 animals, notably the mammals, birds, and reptiles, or amphibia. 

 We shall attempt to place before the reader an outline of the 

 results that have so far been obtained. 



Of all the Vertebrata, we are best acquainted with the 

 mammals. And yet our zoologists differ very widely in 

 respect to the number of their species, though the calcula- 



