572 Dr. F. A. Dixey's reply to Mr. G. A. K. Marshall 



There is no need to multiply instances, though it could 

 readily be done. The point required is to recognise the 

 fact that a mimetic chain can be built up by successive 

 small steps, each of which secures at once the condition 

 which Mr. Marshall himself maintains is favourable to the 

 Miillerian relation ; for he allows, as we have seen, that 

 when the association is once formed, the advantage to all 

 parties, whatever the relative numbers, can be demon- 

 strated by arithmetic. 



This first concession, when followed out into its conse- 

 quences, appears to me of itself sufficient to dispose of the 

 only serious objection brought on a pricri grounds against 

 the possibility of Miillerian approach, whether from one 

 side or from both, even in those cases where both species 

 may be equally "dominant." But if this were not so, 

 Mr. Marshall's second concession (p. 103) would really 

 give me all I want, for by it he asserts the possibility of 

 the very interchange tliat I have all along been holding 

 in view. I am not disposed to raise a controversy about 

 the mere use of words, and if Mr. Marshall prefers his own 

 term "Alternate Mimicry," I have no objection to offer; 

 the point is that he allows the same possibility that I 

 maintain ; the occurrence, that is, of a give-and-take pro- 

 cess between so-called "mimic" and "model." This is 

 the essence of what has been called Reciprocal Mimicry 

 or Diaposematism, for which terms I could suggest no 

 more suitable definition than " the interchange of charac- 

 ters between distasteful forms in virtue of their distaste- 

 fulness." No one could suppose that every step from the 

 one side is exactly in point of time coincident with a step 

 from the other ; nature works on successive individuals, and 

 whether or not at any given moment the general trend is 

 in one direction rather than another is immaterial. More- 

 over, it is conceivable, even on Mr. Marshall's principle, that 

 the tendency might take opposite directions at the same 

 time in different parts of the area of distribution. 



Particular Instances of Diaposematism. 



So much for the attempts that have been made to im- 

 pose limitations a priori on the scope of Miillerian mimicry, 

 and in especial to disallow the possibility of that inter- 

 change of features between distasteful forms which is known 

 as Diaposematism or Reciprocal Mimicry. I now turn to 

 the particular criticisms which Mr, Marshall makes on the 



