tlie colours of certain Lcp'idoptcra. 477 



dark stone, and light on a light one. Which is the 

 more improbable hypothesis, — that the light form, now 

 nearly always withheld, originally possessed a protective 

 significance like the dark form of the same species, and 

 the corresponding light form of the nearly allied V. io, — 

 or that one form of one species stands on an utterly 

 different biological level from all the rest ? I think it far 

 more likely that " all zoological science will be thrown 

 into confusion" by such gratuitous assumptions than 

 by any attempt I have made to suggest, with all due 

 caution, a possible environment in the past history 

 of the species with which the golden form may have 

 harmonised. 



I still hold, and on far stronger grounds than formerly, 

 that all the changes are, or were, in the direction of con- 

 cealment ; that the golden appearance applied chiefly 

 to some former environment, or one which may still 

 exist in other countries ; that in one species {V. io) it 

 has been almost replaced by the green variety, while it 

 has been hidden by the habits of another {V. atalanta), 

 and removed from the darkest forms of all Vaiiessiclce ; 

 that in V. urticce it occasionally occurs on the natural 

 food-plant, and is still protective, in that it is less 

 conspicuous in this situation than the dark form would 

 have been ; but that the latter is so far more effective in 

 promoting concealment that the larvte have developed a 

 strong instinct to wander, and are rarely found on the 

 nettle-plants in the healthy state. 



This whole question is considered by Mr. Bateson to 

 be an " unprofitable field for study " : he may have found 

 it so ; but any attempt to limit the investigations of 

 others by the barrenness of his own experience, cannot 

 be tolerated. It has been the guidance of this hypothesis 

 of the protective value of the colour-changes which has 

 chiefly directed me to seek the forms which are most 

 suitable for the purposes of this enquiry, and to apply 

 the most efficient experiments, and so to accumulate facts 

 which have an interest far beyond their relation to the 

 hypothesis itself. 



