12 COLLEMBOLA OF MINNESOTA 



and that one of five millimeters is a veritable giant among the 

 Collembola, it may readily be imagined how nice are the distinc- 

 tions which must be looked to for species determination. 



It is rather difficult to realize at the outset that a character 

 which will hold true and invariable, and therefore of prime im- 

 portance in separating the species of one genus, may be so 

 variable in another genus as to be absolutely worthless. Thus, 

 while color is in some genera of little value as a specific dis- 

 tinction, in others it alone would serve to identify species. 



In a group which exhibits, throughout, such a tendency to 

 atrophy of ocelli, it is not surprising that genera should have 

 been founded upon the number of ocelli, or, in other words, 

 upon the particular stage to which the ocellar atrophy had pro- 

 gressed. It was almost inevitable that the intervening stages 

 would sometime be found and that the genera founded on 

 nothing more than specific characters would have to be aban- 

 doned. This point will receive further consideration under the 

 difi^erent families. 



Before taking up the more technical portion of this report 

 it may be well to say a few words about the methods found use- 

 ful in collecting and preserving Collembola for study. 



