114 NATURAL SCIENCE [August 



algae, the difficulty of arranging the species into genera and families 

 is extraordinarily great, since there has been an enormous multi- 

 plicity of species production. There exist, between the species 

 typical of the various genera, numerous other forms, varieties, etc., 

 each of which is a perfectly constant type, but which confuse the 

 limits between genera and families. Very soon the dictum which 

 I laid down in connexion with my systematic working up of the 

 Flagellata in 1892, will apply equally well to the algae, namely, 

 that the more we take into consideration the multitude of forms, 

 the more difficult to construct and the more artificial our system 

 becomes. The contradiction between the constancy of the single 

 form, whether we call it species or variety, and the variability of all 

 characters within the limits of an extended circle of forms, be it 

 genus or family, has not yet been explained ; Darwinian teaching 

 has brought clearly to light the existence of this contradiction, but 

 it has not yet discovered how to resolve it. 



Geobg Klebs. 



