THE HISTORY OF UYKMECOLOGY. 131 



they occur. Such a species is Catnponotus inacnlatus, which occurs 

 on every continent and many islands, and varies ad infinitum. In study- 

 ing such species we are often presented with two sets of variable 

 characters, one of which is adaptive and largely morphological, while 

 the other comprises small indifferent traits of no considerable value to 

 the organism in its struggle with its environment, 

 such as slight peculiarities in size, sculpture, pilosity 

 and color. These characters, which remind one of 

 the De Vriesian " unit characters," are relatively 

 stable in particular races or varieties and have a 

 tendency to combine and recombine in endless 

 permutation. Besides C. inacnlatus, many of the FlG 75 Head 



species of the large genera Formica and Pogo- of female Epitritus 



, , , , r ,, , e mince of the West 



noiuynnc.r are admirable examples of this phe- Indies . (Original.) 

 nomenon. 



Characters of importance in classification may be drawn from all 

 parts of the ant's body, but the most useful are furnished by the number 

 of palpal joints, shape of the clypeus, mandibles, shape and compara- 

 tive length of the antennal joints, shape of the thorax, petiole, post- 

 petiole, spurs of the middle and hind tibia?, tarsal claws, genitalia of the 

 male, the venation of the wings of both sexes, the structure of the 

 gizzard, larva and pupa. The tribes, genera and species are built on 

 combinations of these characters. But as there are many minor charac- 

 ters, especially in sculpture, pilosity and color, which though constant 

 for all the members of a caste, may nevertheless vary in colonies in 

 different localities, it becomes necessary to recognize smaller divisions 

 than that of the species. These subdivisions are of different rank 

 for the reason that slight differences in form or sculpture are more 

 important, because less variable, than pilosity and coloration. Mvrme- 

 cologists have therefore recognized two categories within the species, 

 one more important and called the race by Forel, the subspecies by 

 Emery, and another less important category which has been called the 

 variety by both of these authorities. Subspecies may be regarded as 

 small or incipient species in the De Yriesian sense. They are much 

 less frequently connected by transitional forms than the varieties. 



The recognition of these various categories necessitates the employ- 

 ment of a quadrinomial nomenclature. Thus one of our common 

 carpenter ants is known as Caiuponotus herculeanus Linn, subsp. lif/ni- 

 perdus Latreille var. noveboracensis Fitch. This is a strictly North 

 American variety, with red head and thorax, of a smooth race, or sub- 

 species, of the dark-colored, opaque, circumpolar species lierculcanns 

 the typical form of which is confined to Europe. This method of 



