CHAPTER XII. 



DISTRIBUTION. 



104. THERE is a distribution of organisms in Space, and 

 there is a distribution of organisms in Time. Looking first 

 at their distribution in Space, we observe in it two different 

 classes of facts. On the one hand, the plants and animals of 

 each species, manifestly have their habitats limited by ex 

 ternal conditions : they are necessarily restricted to spaces 

 in which their vital actions can be performed. On the other 

 hand, the existence of certain conditions does not determine 

 the presence of organisms that are the fittest for them : there 

 are many spaces perfectly adapted for life of a high order, 

 in which only life of a much lower order is found. While, 

 in this inevitable restriction of organisms to environments 

 with which their natures correspond, we find a negative 

 cause of distribution ; there remains to be found that positive 

 cause of distribution, whence results the presence of organ- 

 isms in some of the places appropriate to them, and their 

 absence from other places that are equally appropriate and 

 more appropriate. Let us consider the phenomena under 

 these categories. 



105. Facts which illustrate the limiting influence of sur- 

 rounding conditions, are abundant, and familiar to all read- 

 ers. It will be needful, however, here to cite a few typical 

 ones of each order. 



