THE CATEGORIES OF VARIANT INDIVIDUALS 63 



seemingly distinct species, should be referred to by a symbol 

 rather than by a specific name. 



It must be remembered that not a great deal is known 

 concerning the hereditary stability of species. It has always 

 been assumed, since the contrast between hereditary and non- 

 hereditary characters was realised, that the characters of the 

 species were hereditarily stable. Naturally few taxonomists 

 have had the time or opportunity to breed out the members of 

 groups which they have confidently described as species. A 

 substantial number of described species are forms of dubious 

 hereditary stability. ' Environmental forms ' are often given 

 distinct specific names, as in the case of Artemia salina and 

 A. milhauseni and in various groups of Cladocera and Mollusca 

 (e.g. cf. Miller, 1922). Finally, in claiming a general validity 

 for taxonomic procedure in the treatment of species as distinct 

 groups, we recognise that this claim must be limited by the 

 admission not only that such groups are of various degrees 

 of distinctness in the number of divergent characters, but also 

 that sometimes intergradation between the various elements 

 in a population may be so complete as to render the limits 

 between species purely arbitrary. 



Within the species itself systematists are accustomed to 

 recognise certain subdivisions — the subspecies, the variety, 

 and less frequently the form and the race. At the present 

 time the terms variety and subspecies are both used for the 

 major subdivisions of the species, but speaking generally they 

 have a different connotation. The subspecies is a term in 

 regular use among mammalogists and ornithologists, and it 

 is used essentially to denote a geographical entity, the major 

 subdivisions of the species of birds and mammals having 

 usually distinct geographical ranges. The term variety, 1 on 

 the other hand, though it is used for a major division of the 

 species of invertebrate animals, has no such geographical 

 implication. In many invertebrate groups the subdivisions 

 are types which occur sporadically throughout the range of 

 the species, and though in morphological status they correspond 

 to the subspecies of birds and mammals, the accidental 



1 Rothschild and Jordan (1903) have used the term variety not for any 

 particular category of the components of a species, but for ' all the members of 

 a species indiscriminately.' The different categories of varieties are given special 

 names or symbols. 



