mean of the typical species, and which usually are eliminated 

 in the struggle for existence, but which occasionally manage 

 to reach the final stage of the species. Such " sports " are, 

 in their most marked forms, the true " discontinuous varia- 

 tions " of Bateson, and it is rather remarkable that certain 

 modern evolutionists appear inclined, contrary to the 

 generally accepted view, to look upon these discontinuous 

 variations as not only of equal, but of even greater impor- 

 tance in the evolution of species than the smaller individual 

 differences existing between the more typical forms. 



It may be well before going further to obtain some definite 

 and clear limitation to the term "discontinuous variation," 

 which is coming into common use in our magazines and in 

 the daily conversation of entomologists. It appears that the 

 term is often misapplied, and one is inclined to think that 

 the author of the term uses it in so wide a sense that it in- 

 cludes many cases widely differing in their essence. The 

 black Amphidasys bctnlaria ab. doublcdayaria, is often quoted 

 as one of the most marked cases of discontinuous variation, 

 but is it really a case of discontinuous variation at all? It 

 is well known that in some broods, reared in confinement, 

 the progeny have separated distinctly into two portions, one 

 of the typical " peppered " form, the other of the " negro " 

 aberration, with scarcely any trace of what might be termed 

 intermediates. On the other hand, other broods have given 

 a graduated series from the pale to black, the examples 

 showing a regular gradation of forms varying but little from 

 those nearest, but leading from one extreme to the other. 

 Apart from the fact, however, that an abundance of inter- 

 grading forms do exist, it may be well to ask those that call 

 the "black" aberration a marked instance of discontinuous 

 variation, whether it be really so ? It occurs to me to ask 

 whether this change from grey to black is so discontinuous 

 as at first sight it appears? Of course the apparent change 

 from white to black, as measured by the human sense of 

 sight, is a great one ; but is the change from a white or 

 whitish grey to a black scale in A. bctnlaria a great one, or 

 so discontinuous as it appears? On the other hand, is it 

 not the simplest change that can take place, due to a primary 

 modification of the chemical condition of the scale contents ? 

 That there is an abundance of intermediate forms, with a 

 fewer or greater number of black scales, does not vitiate the 

 suggestion, but rather increases its value ; for as the change 

 is possibly due in this case to increased vital activities, it is 

 to be expected that intermediate stages will exist and inter^ 



