§84 FOUR-FOOTED AMERICANS 



"Yes, they are very common, at least, through the 

 half of the country eiist of the Mississippi. They feed 

 chiefly at night, which is probably the reason you have 

 not noticed, them." 



" Then people who live the other side of the Mis- 

 sissippi are not bothered with them ? " said Nat. 



" They may not have this particular ^leadow jNIouse, 

 but there is sure to be a near cousin for every part of 

 the country, and one for every day in the year too. 

 Why, aside from all the other gnawers, there are two 

 hundred species in the family of Rats and Mice alone." 



" What makes a species ? " asked Nat. 



" One fine day, long ago, some Meadow Mice from a 

 certain place might have been accidentally carried far 

 away from home to a place where the food and country 

 and climate were entirelj^ different from where they 

 were born. They had to change their habits a little to 

 suit their new home, and after many generations this 

 change of habit made a change in their looks. Their 

 feet might be larger, or they might have grown a new 

 pattern in coats. Then some Wise ]\Ian noticed this 

 and said, ' Here is a new species.' So the Wise jMen who 

 are trying to draw the family tree of these nuisance 

 animals cannot finish it yet, because, no matter how each 

 one works on his tree, someone else is always going 

 out and finding new species that must be added as 

 twigs." 



" Then I guess we can't learn all the names of that 

 family," said Dodo. 



" No, indeed. There are about ten species, however, 

 belonging in different parts of the country, whose pict- 

 ures I can show you and Avhose names you must try to 



