proceedings: biological society 235 



groups of organisms. It had been impracticable to include a discussion 

 of the very interesting categories, known as physiological species or 

 races, such as the parasitic fungi, among which are races that appear 

 identical morphologically but which are confined to certain host plants, 

 each to each, or such as the bacteria, many forms of which appear 

 identical morphologically but which cause distinct physiological effects, 

 either chemically on artificial substrata, or biologically in producing 

 diverse diseases of plants and animals. Mr. Hitchcock further stated 

 that much of our difficulty in determining whether a given form repre- 

 sents a species or a subdivision of a species results from our ignorance. 

 We do not have sufficient facts. If we are compelled to draw con- 

 clusions from a single specimen in a herbarium or even from several 

 specimens we can give only an opinion as to the relation of this form 

 to others, an opinion strengthened, it is true, by training and experience, 

 but at best only an opinion. If we have all the facts, or enough so 

 that lacking data may be safely ignored, our problem is to interpret 

 results and define relations. 



Mr. N. HoLLisTER said: Nearly all systematic mammalogists 

 now distinguish subspecies from species by the test of intergradation : 

 some workers insist upon an actual blending of characters over con- 

 tinuous range between typical subspecies, while others admit what 

 is known as "intergradation of characters," even between insular 

 forms, to be sufiicient reason for the use of the trinomial. Old con- 

 ceptions of what is a species are now lightly considered, and authors 

 are frequently inconsistent in their treatment of forms. A good defi- 

 nition of a species was given a few years ago by one writer who stated 

 that "a species is a thing described as such." The same kinds of 

 characters, or precisely the same character, may serve in different 

 instances for distinguishing subspecies, species, or even genera. The 

 difference in the number of the enamel folds in the last upper molars 

 of the capybaras of Surinam and Paraguay was cited as a case where 

 a character sometimes of generic weight serves only to separate sub- 

 species. Specimens showing the process of the loss of one fold are 

 found in Brazil midway between the two typical races. It is a com- 

 mon experience for the monographer working with material assembled 

 from many collections to reduce numerous described species to the 

 rank of subspecies; the forms so treated still retain exactly the same 

 characters that served them as full species. 



Dr. H. C. Oberholser spoke on the question from the standpoint 

 of an ornithologist. He said: Most ornithologists at the present 

 time regard the distinction between a species and a subspecies as one 

 of the presence or absence of intergradation. In other words, a sub- 

 species is an imperfectly segregated species — a form occupying a separate 

 geographic area and intergrading with some other form. This inter- 

 gradation may take place: (i) by gradual change over contiguous 

 geographic areas; (2) by an abrupt change in an intermediate area; 

 (3) by individual variation, whether or not the ranges of the two forms 

 adjoin. The amount of difference does not constitute the distinction 



