TRANSACTIONS OF SECTION D. 519 
showed illustrations and specimens of a few cases of mimicry in temperate North 
American butterflies, and pointed out what he believed to have been the evolu- 
tionary history. If this history be correct, then it is impossible to explain the 
resemblance as due to the influence of environment, because recent invaders from 
the Old World into this region have caused the mimetic modification of in- 
digenous species. According to theory of environment the invaders ought to 
have been modified instead of the residents. 
ii) Mimicry between the Genera of certain African Nymphaline Butter- 
y el ymp 
flies. By Professor E. B. Pouuron, F.H.S. 
Although the models for butterfly mimicry in the Old World commonly 
belong to the great distasteful sub-families, the Danaine and Acreine, they 
are also to be found among the groups in which we are accustomed to look for 
mimics rather than models. This is certainly true of the Nymphaline, in which 
the mimicry on both under and upper surface of the blue species of Crenis by 
Crenidomimas is as remarkable as any known example of such resemblances. 
The largest number of such instances, however, have been very little spoken 
of in works on mimicry, although recognised by Aurivillius. I refer to the 
mimicry of the species of Catuna, with both sexes alike, by the females of 
species of the allied genera Huryphene, Diestogyna, and Cynandra. The resem- 
blance has another characteristic of mimicry in general, viz., the development 
of secondary resemblances between the mimics. ‘Thus the likeness between the 
females of Cynandra opis and a Diestogyna, collected by Mr. S. A. Neave in 
Uganda, is positively startling. I have always hesitated to draw attention to 
these examples of mimicry until I knew more about the habits of models and 
mimics, but within quite recent years Mr. W. A. Lamborn, to whom I owe so 
much, has observed in the Lagos District that the mimics actually fly in the 
company of their models.° Examples of models and mimics taken in one sweep 
of the net by Mr. Lamborn and others on which special observations have been 
made by him are exhibited to the Section. 
8. The Term Mutation. By Professor E. B. Pouuron, F.R.S. 
1. The word ‘Mutation’ was originally introduced by Waagen! to express a 
simultaneous and probably gradual change in a relatively large proportion of the 
individuals of the species, if not the whole species. ‘ Mutation’ expresses the change 
itself, not the process by which it has been produced. Waagen nowhere states that 
his ‘ Mutations’ are discontinuous variations or ‘ Saltations.’ Waagen’s material was 
exclusively paleontological, and his ‘Mutations’ are variations in time. He was 
inclined to believe that they were produced by a developmenta) force resident in the 
organism. 
". ‘Mutation’ was re-introduced by de Vries as equivalent to ‘ Saltation,’? and 
applied to Darwin’s ‘large’ or ‘single’ variations as opposed to his ‘ individual 
differences.’ The latter de Vries called ‘ Fluctuations.’ According to de Vries as well 
as Darwin both forms of variation are hereditary. De Vries distinguished between 
them by supposing that a ‘Mutation’ leaps at once to a new position of genetic 
stability—it is what Galton previously called ‘transilient.? De Vries’ ‘ Fluctua- 
tions,’ on the other hand, are subject to Galton’s ‘regression to mediocrity,’ and 
there is a limit to the advance which can be achieved by selection.? It must be 
added that de Vries is disposed to explain ‘ Fluctuations ’ as due to the action of the 
“Die Formenreihe des Ammonites subradiatus, &c.’ Geogn.-palacont. Beitrage ii, 
Heft 2, b (1869), p. 186. 
* The Mutation Theory, Engl. Transl., Vol. i, London (1910), p. viii. ‘These 
saltations, or mutations. .. .’ 
® Ibid. p. 123 :—‘ Continued selection [of fluctuations] by no means fixes the 
character chosen, but, by separating the race further from the type from which it 
sprang, continually adds to the risk of regression.’ This is precisely Galton’s con- 
clusion, just as ‘ Regression’ in this sense is Galton’s term. Darwin also ‘fully 
recognised the limits which may be set to the results achieved by the artificial selection 
in one direction of individual variations,’ and ‘he admitted the necessity of waiting 
for a fresh “start in the same line,”’ (Darwin and the Origin, Poulton, Londop 
(1909), pp. 48, 49). 
