( Imi ) 
cause for such cases as those that have been mentioned. 
This has been shown so convincingly by Prof. Poulton, that 
I need not enlarge on the point further than to remark that a 
general lightening or darkening of pigment, as in some experi- 
mental cases, is an entirely different matter from the produc- 
tion of an elaborate colour-pattern like that, for example, of 
the female of Perrhybris pyrrha and its Ithomiine and Heli- 
conline counterparts. 
But, it may be asked, if the theory of a direct action of the 
environment be given up, what explanation remains? Well, 
the hypothesis of mimicry remains. This rationalises the 
geographical facts, without raising the difficulties involved in 
the theory of direct action. I will not attempt to recapitulate 
the arguments in favour of the mimetic explanation, but _ 
for my present purpose will assume that it is, at all events 
provisionally, accepted. 
This being so, it will not escape the notice of those who 
inquire into the facts, that there are some anomalies that 
require further explanation. It is, for example, sometimes 
found to be the case that a supposed mimic is observed in 
regions where its model is not known to occur. This may in 
certain instances be due to the ascertained fact that many 
insects, including butterflies, do occasionally extend their 
range, occupying districts where they were previously un- 
known. In the case of a Batesian mimic, such a proceeding 
would presumably be hazardous in the extreme, and the 
species could hardly be expected to establish itself in its new 
home unless it succeeded in developing some fresh means of 
defence. In the case of a Miillerian mimic, the difficulty would 
be lessened. 
But in seeking an explanation of such cases there is another 
factor to be taken into account; viz. the distribution of 
enemies. It is quite conceivable that a migratory bird, for 
instance, which had learned its lesson in one locality, might 
carry its experience into another region; and in this way the 
mimic might still retain some measure of the protection 
originally gained in the presence of its model. An interesting 
example, possibly explicable on these lines, has been adduced 
by Prof. Poulton. An hypothesis of this kind naturally 
