20 THE MAMMALIA. 



prove the theory of descent as improbable and un- 

 necessary, by assuming in its place a general law 

 of development by which the different species origi- 

 nated side by side without blood-relationship. His 

 fundamental idea, as he himself says, is that with 

 the first origin of organic matter and of organisms 

 a plan of development was also given, a whole 

 series of possibilities (by whom ? we ask), but that 

 various outward influences acted determinatively 

 upon individual development and produced a dis- 

 tinct character. That organic nature is the result 

 of some grand plan of development and of universal 

 laws, and that the explanation of the processes of 

 development is nothing more than that they take 

 place according to internal causes, according to 

 laws by which the organisms are most distinctly 

 forced to an ever higher form of development. In 

 like manner eggs and germ cells are said to pass 

 into new forms from internal causes : indepen- 

 dent, living, youthful forms are said to begin a 

 development different to the typical one, while out- 

 ward influences affect the process in various modi- 

 fying ways, and transformations ensue which, 

 although contained in the general plan, did not all 

 necessarily need to be fulfilled. Every different 

 species is said to have originated in this way by it- 



