INDIVIDUALS AND SPECIES 31 



systematic science are of a special kind. We must 

 catalogue our materials. We must develop a rea- 

 sonably definite idea of the various species making 

 up the organic world, and in doing so we cannot 

 conveniently express a fluctuating unit. It is this 

 need for stability which has caused most of the 

 trouble with the idea of species. 



Gregory has attempted the expression of an un- 

 defined taxonomic unit by proposing the term cir- 

 culus for the groups of individuals centering about 

 a definite association of characters.^ The concept 

 is valid, but it amounts to no more than another 

 definition of the species concept of all time, hence 

 a new term is unwelcome. For the purposes of 

 taxonomy Montgomery's proposal that the species 

 is a mental cross-section of a line of evolution 

 appeals to me as the most valuable idea yet ex- 

 pressed.^ Elsewhere ^ I have considered more 

 fully the practical aspects of this matter in tax- 

 onomy; this much is adequate for my present 

 purpose. 



Given an entity, the species, made up of many 

 lesser entities, the individuals, we have an ade- 

 quate foundation for the consideration of problems 

 of evolution, but it is desirable to clarify these con- 

 cepts still further by the consideration of another 

 step in the association of organisms. In a number 

 of cases, notably among the insects, the relation of 



' Mason, F., Creation by Evdvtion, 1928. * Op. dt. •* Op. cit. 



