294 



PRINCIPLES OF ANIMAL BIOLOGY 



From this description it appears that the prairies are intermediate 

 between the forest regions and the plains in the same way as a checker- 

 board is intermecHate between a plain white board and a bhick one. 

 The checkerboard is not gray, but a patchwork. While on a map of 



<^"d. 



35 to 40 indies. 

 More than 40 " 



Fig. 205. — Annual rainfall in the lower part of the state of Michigan. Tliis illustrates 

 the differences in physifal conditions which may prevail even in relatively small areas. 

 {After C. F. Schneider, Pub. 9, Mich. Gcol. and Biol. Surv.) 



distribution typical plains animals and typical forest animals would 

 occur together and so appear to indicate intermediate conditions, these 

 forms tend to be distributed as an inlay or mosaic. 



