20 THE MAMMALIA. 



prove the theory of descent as improbable and un- 

 JSary, by assuming in its place a general law 

 of devi lopment by which tin- different species origi- 

 i >ide by side without blood-relationship. His 

 fundamental idea, as be himself -ays, is that with 

 the iirst origin of organic matter and of organisms 

 a plan of development was also given, a whole 

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

 'iis outward influences acted determinative ly 

 upon individual development and produced a dis- 

 tinct character. That organic nature is the result 

 of some grand plan of development and of universal 

 . 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 organism^ are most distinctly 

 forced t<> an ever higher form of development. In 

 like manner eggs and germ cells are said to pass 

 m-w forms from internal causes: indepen- 

 dent, living, youthful forms are said to begin a 

 devrl.. pm, ;it different to the typical one, while out- 

 ward inthh nces affect the process in various modi- 

 fying and transformations ensue which, 

 although contained in the general plan, did not all 

 necessarily need to be fulfilled. Kvcry dim-rent 

 have originated in this way by it- 



