OF WASHINGTON, VOLUME XV, 1913 119 



subgenus species or subspecies of others or even a variety in the 

 mind of the extremist who insists on the widest range for specific 

 and generic characters. In an effort to define the distribution of 

 such a complex, what are we going to do? Who are we going to 

 accept as the authority? Naturally we will be inclined to accept 

 the one who is nearest in accord with our individual opinions. If 

 we are familiar with the genus or species, as the case may be, per- 

 haps our opinion will be worth something as to the range of dis- 

 tribution, but suppose we are not familar with the genus or species 

 of one author although we may be an authority on some other 

 group, and we want to compare the distribution of his concepts with 

 what we consider be to a species in our special group. In such a 

 case our conclusions as to the governing factors in the distribution, 

 will not be worth much beyond those based on our own interpreta- 

 tion of a species and personal knowledge of the range in its distri- 

 bution. Yet broad generalizations have been based on just such 

 uncertain data by biologists and zoologists in the past and will be 

 in the future until some common standard is established. 



If the leading biologists would meet on some common plane of 

 reasoning by withdrawing from their fortified positions of extreme 

 opinions (under a flag of truce if necessary), and would be guided 

 by a sincere desire to get together on some of the more essential 

 evidences and facts as to the units for comparison, something of real 

 importance and value would be accomplished. 



There has been a great deal of speculation on the probability 

 that certain widely separated land masses of two continents were 

 connected at some remote period, because of the presence in both 

 areas of the same or similar genera and species. 



The theory of circumpolar distribution during periods of uni- 

 form mild climatic conditions and of separations and isolations 

 during the frequent glacial disturbances is a most attractive one 

 considered by many to be a simple explanation of the occurence of 

 the same genera and species in the boreal and temperate zones of 

 two continents. 



Undoubtedly the periods of glaciation which prevailed at various 

 geological times in different parts of the world have had a marked 

 influence on the distribution of plants and animals and especially 

 certain discontinuous distribution. It is evident, however, that a 

 number of examples in glaciated areas, in addition to those in areas 

 out of the range of glacial influences, can not be explained by the 

 glacial theory of distribution. 



In looking for examples of discontinuous distribution, I must 

 naturally give first consideration to insects and to the group of in- 

 sects which has received my special attention, namely, the Scolytid 

 beetles. 



