SECOND EVENING DISCOURSE. 737 
It seemed desirable to seek for further confirmation of the truth of Fritz 
Miiller’s interpretation, and this the lecturer has made it his business to do, It 
appeared to him that if the Miillerian theory were valid, certain consequences 
ought to follow. Did these consequences follow or did they not ? 
(1) It is obvious that in Batesian or true mimicry the advantage is all on the 
side of the mimic. Experience gained by tasting the mimic would be used to the 
injury of the model. hile therefore there is every inducement for the mimic 
to seek safety by approaching nearer and nearer to the aspect of the model, 
there is no reason for the model to assimilate itself to the mimic, but rather the 
contrary. 
In a Miilerian association, on the other hand, the benefit is mutual. Each 
fresh accession to the group is a source of strength, not of weakness. Everything 
is in favour of the formation of such groups as rapidly and on as large a scale as 
possible; hence there is nothing to impede, and everything to promote, the free 
interchange of characters all round, each ember being able to act, so to speak, 
as both mimic and model. This could not happen, as has been shown, in the case 
of Batesian mimicry, 
Several instances of such reciprocity or interchange of features have been 
detected by the lecturer, and others have since come to light. From what has 
gone before, it is clear that such cases, inexplicable on any other theory, tend to 
establish the validity of the Miillerian hypothesis. 
(2) A further consequence of the mutual influence exercised by the constituents 
ofa Miillerian group is this: it ought sometimes to happen that two species, though 
both influenced in common by a third, will show a nearer approach to each other 
than either does to the common model. As a matter of fact this is found actually 
to occur in Nature, and fresh evidence is thus supplied for the validity of the 
Miillerian interpretation. This phenomenon, again, could not happen in Batesian 
mimicry. Two true or Batesian mimics of the same model could nct influence 
each other; they could only be influenced in common by their model. 
(3) Finally, the fact that each distasteful form is capable of affording protection 
to forms on each side of it may be expected to favour the existence of gradational 
groups; distasteful forms, with perhaps little or no resemblance between them, 
being held together, as it were, by a chain of distasteful intermediates. This also 
has been found to be the case, many of the mimetic groups in a given zoological 
region forming together a kind of nexus, each node of which may be occupied by 
a dominant group or species showing a very different colour-scheme from the 
occupants of the other nodes, while the uniting strands of the network are con- 
stituted by a more or less completely gradated series of transitional forms. 
It will be seen from the foregoing how far we have advanced beyond the 
original conception of Bates, and it must be allowed to be a striking fact that the 
progress of recent investigation has uniformly tended to supply fresh confirma- 
tion of those developments of the theory of mimicry which have traced their 
origin from the fertile suggestion of Fritz Miiller. 
1907, 3B 
