( X ) 



change which so often occurs in a species with a wide , 

 phical range, ultimately splitting it up into subspecies and 

 true species, would draw the associated forms after it by the 

 operation of the very principles by which the group was 

 originally formed. If this process were sufficiently gradual 

 no principle of Mullerian association need be violated. Or 

 the facts might be reasonably explained in another way : the 

 dominant (a word which here implies only the commonest 

 and best known, in fact, the most widely advertised 

 of the specially defended Lepidoptera of the district) 

 form might have inhabited the region in question, and 

 assumed its peculiar aspect before the formation of the 

 group, and may have then separately "converted " each new- 

 comer as it arrived in the district. The tendency of a group 

 was certainly, as Mr. Blandford maintained, to extend its 

 limits indefinitely — a tendency which had operated with great 

 success in certain cases. But the spread of species always 

 encountered opposing forces which in many cases acted as 

 effective barriers. 



With regard to Brunner's " Hypertely," he maintained 

 that one knew far too little of the details of the struggle for 

 existence to justify the conclusion that it was incompetent to 

 produce such effects. What little was known confirmed the 

 belief that very minute differences might serve to turn the 

 scale. The differences between extremely perfect resem- 

 blances and those which were less perfect or only very rough, 

 were probably to be explained by the relative age of the 

 association in the former, or the more complete and rapid 

 operation of natural selection on account of a special reliance 

 on this among other modes of defence possessed by the 



{aiv, together ; olttS, away : arrjua, sign) colours, pattern, or appear- 

 ance, the noun being Synaposeme. They may also be said to possess 

 Mullerian Warning Colours or Common Warning Colours. For 

 those extremely interesting but, as I believe, relatively uncommon 

 cases, in which the approach is mutual — a process of " give and 

 take,'' so well described by Dr. Dixey — the term Diaposematic 

 (Sid, used to express mutual relation, as in " dialogue,'' anS, and (rrjua) 

 may be employed, the noun being Diaposeme. These cases may 

 also be spoken of as Reciprocal Warning Colours. Mr. Arthur 

 Sidgwick has kindly helped in the formation of these new terms. 

 — E. B. Poulton, Jmie Uth, 1897. 



