which I referred when dealing with the Java Pieridae where I applied the term 

 " persistent " to these spots which I looked upon as being portions of the wing 

 surface where the original colour had resisted the evolutional invasion of black 

 much longer than in other parts, the cause whereof must probably be sought 

 in some special condition of the tissues. However this may be, it is certainly 

 reasonable to assume that when in the stress of the process of colour evolution 

 the black pigment endeavours to spread over the original colour and encounters 

 such a disturbance, induration, or persistent spot, this pigment will be distributed 

 around it and an island will be formed of the original colour surrounded by 

 black. We find in fact that the colour of this enclosed centre accords with 

 this proposition as a rule, sometimes, however, circumstances may arise when 

 this is not so clearly perceptible. In the ocelli of Parnassii the centre 

 frequently exhibits for the greater part the original red colour, only just in part 

 faded to white. In the various genera, however, in accordance with the same 

 absence of uniformity, invariably to be witnessed in the course of an evolutionary 

 process, the process in question has doubtless frequently taken a special course. 

 Thus, for instance, it is remarkable how these ocelli on the hind-wings of 

 Parnassii correspond in form and manner of disposition to the black spots on 

 their fore-wings ; the former are evidently just such spots as the latter in which, 

 however, the black pigment has not been distributed to the same extent and 

 where, consequently, in the formation of the ocelli the black pigment has not 

 exercised as much stress as has been the case in other genera. In some 

 Satyridae the course of this process can be clearly discerned. The accom- 

 panying illustration (PI. XV fig. 506) gives an enlargement of the ocellus, indicated 

 on PI. XV fig. 30rt by number 5, on the under surface of the hind-wings of 

 Cyllo Leda L. a clear white centre will there be observed round which a 

 fairly wide ring of intense black has gathered while outside this again a narrower 

 yellow ring has been formed. Now this centre is doubtless the vestige of the 

 induration or persistent spot where the original colour was not — or at least not 

 completely — covered by the black pigment, but where this has gradually faded 

 to white in conformity with the rule of the process of colour evolution or has 

 already been destroyed and replaced by scales simply filled with air which, in 

 view of the intensity of this white, I do not consider improbable. 



For this reason it not unfrequently happens, as Bateson observes, that the 

 centres of ocelli are deficient in or destitute of scales. Around this centre the 

 black pigment, which was checked in its even distribution, has become accumu- 

 lated, thereby causing the production of a fairly broad ring of black much more 

 intense than the black pigment occurring elsewhere in the colour of the wings 

 in this species. This intensity clearly indicates that an accumulation of this 



