248 Retrograde Varieties 



formerly lost. Some may originate in a 

 negative, others in a positive manner, but in 

 both cases nothing really new is acquired. 



This distinction holds good for all cases in 

 which the relationship between the forms in 

 question is well known. It seems entirely justi- 

 fiable therefore to apply it also to cases in 

 which the systematic affinity is doubtful, as well 

 as to instances in which it is impossible to ar- 

 rive at any taxonomic conclusions. The ex- 

 treme application of the principle would no 

 doubt disturb the limits between many species 

 and varieties as now recognized. It is not to be 

 forgotten however that all taxonomic distinc- 

 tions, which have not been confirmed by physi- 

 ologic tests are only provisional, a view ac- 

 knowledged by the best systematists. Of course 

 the description of newly discovered forms can 

 not await the results of physiologic inquiries, 

 but it is absolutely impossible to reach definite 

 conclusions on purely morphologic evidence. 

 This is well illustrated by the numerous dis- 

 cords of opinion of different authors on the sys- 

 tematic worth of many forms. 



Assuming the above mentioned principle as 

 established, and disregarding doubtful cases as 

 indicated, the term progressive evolution is 

 used to designate the method in which element- 

 ary species must have originated. It is the 



