12 ENTOMOLOGICAL NEWS [Jan., '14 



requirements put upon them by varying natural conditions, or 

 failing to meet them perish. 



This phase of biologic inquiry can, in a measure, be likened 

 to infinity. In theory infinity is incomprehensible, but we com- 

 prehend parts of it in practice. Theoretically there is almost 

 no limit to the morphologic variety that life may assume, but 

 practically it is limited to such morphology as we know or can 

 base on that which is known. When we come to consider the 

 limits of species we find that in practice as well as theory they 

 have among themselves no natural sequential or genetic limits, 

 and often no residue limits at any given point in their develop- 

 ment, but nevertheless they certainly exist under both condi- 

 tions, however obscured may be their limits. Were we able to 

 restore and gather together all the individuals that have arisen 

 during the evolution of species on this globe up to the present 

 day, we would find few or no places where we could draw 

 natural lines of division between categories of individuals. In 

 practice, however, among the living residue of today, the limits 

 of natural species are such as they make for themselves. It 

 remains for us to find these limits out. The illustrations which 

 I have used may be judged as forced and far-fetched, but they 

 are true to nature and therefore their forcefulness is the more 

 serviceable. 



Variation even among existing forms has almost no limits. 

 The number of possible combinations of the characters of 

 organisms, past, present and future, is almost infinity itself. 

 The best that we can do in the present with the great plastic 

 mass of living young forms is to divide it as conveniently as 

 we may, conforming to phylogenetic lines as closely as it is 

 possible to interpret them. It is certain that in highly special- 

 ized and comparatively recent groups we gain simplicity and 

 conciseness as we descend in the taxonomic scale and diminish 

 the scope of our units of treatment. This applies not only to 

 groups but to genera, subgenera, species, subspecies and races. 

 It arises from the contraction of taxonomic values obtaining 

 in such stocks. We need to apply a restricted species-concept 

 in dealing with these forms, as well as employ restricted groups 

 and categories in general. 



