318 THE THEORIES OF EVOLUTION 



are to be considered as internally formed of a host 

 of units, partly active and partly inactive. Ex- 

 tremely minute and almost inconceivably numerous, 

 these units must have their material representatives 

 within the most intimate parts of the cells." 



"Therefore we can consider the following as the 

 principal difference between elementary species and 

 varieties; that the first arise by the acquisition of en- 

 tirely new characters, and the latter by the loss of ex- 

 isting qualities or by the gain of such peculiarities as 

 may already be seen in other allied species." 



Mutation can take place in the line of progression or 

 in the line of retrogression according to whether char- 

 acters have been acquired (have been awakened) or 

 have been lost (have become latent) . 



Among the forms obtained by De Vries, some were, 

 according to his standard, true species, while some 

 others were regressive varieties, that is, they presented 

 no other peculiarity but the passing of one certain 

 character into latency. 



"V. The same new species are produced in a large 

 number of individuals. This is a very curious fact. 

 It embraces two minor points, viz: the multitude of 

 similar mutants in the same year, and the repetition 

 thereof in succeeding generations. Obviously there 

 must be some common cause." 



"VI. The relation between mutability and fluctu- 

 ating variability has always been one of the chief 



