( cxl ) 



dealt with on the present occasion. Certainly there exist 

 among the Pierines, as we have seen, structures which bear 

 the appearance of ordinary scales just beginning to take on 

 the special features of plume-scales. Such may be seen in 

 Euchloe, Euterpe, Neophasia and elsewhere. The accessory 

 disc appears to be a form of specialisation characteristic of 

 the Pierinae, and it is natural to conjecture that those Pierine 

 forms in which the disc is absent or ill -developed are the 

 earlier. But it is not always easy to determine whether 

 apparent simplicity of structure is ancestral or the result of 

 degradation ; and it would be hazardous in the extreme to 

 pronounce, for instance, that the feeble development of the 

 disc in Leptophohia is an indication of high antiquity in that 

 genus. At the same time, I venture to think that in both 

 Euchloe and Keoj^hasia we have early Pierine genei-a, the 

 ancestral condition of which is in some sort represented by 

 their plume-scales. The apparent absence of these structures 

 from such presumably early genera as Eucheira and Metaporia 

 is noteworthy ; embryological investigation might possibly 

 determine whether in these genera they ever existed. The 

 remarkable scale of the African Mylothris, so often mentioned, 

 is comparatively simple ; but I am inclined to consider its 

 simplicity as due rather to specialisation than to the persist- 

 ence of ancestral conditions. It is obvious that we have 

 here touched upon a subject that calls for much fuller 

 investigation. 



I should wish, before conckiding, to put in a word of caution. 

 The nature of the facts dealt with in the present address is 

 such that it has not been possible to avoid a certain appear- 

 ance of dogmatism. No one can feel more strongly than I 

 do that dogmatism is, as a rule, out of place in science ; and 

 I do not wish my statements to be taken as more than the 

 nearest approach to truth that I have been able to make after 

 a long-continued investigation. I am quite sensible that my 

 results ought to be checked by other observers ; and that 

 some, perhaps many, of them will require subsequent modifi- 

 cation. In several instances I have had to depend on the 

 examination of single individuals, and it has not been possible 

 for me to be sure that these examples were truly represent- 



