406 MR. E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
in unserem Urwalde Gestein nirgends zu Tage tritt, ist bei diesen grossentheils an 
Urwaldsbiiutnen lebenden Arten wold kaum an Aehnlicbkeit mit mineraliscben 
Substanzen zu denken. Alle Puppen, die ich irn Freien an Pflanzen zwiscben Laub 
gefunden babe (z. B., Morpho, Caligo, Prepona, Siclerone, Catanephele), sind griin, 
mit Ausnahme von Acrcea (ungeniessbar), deren Puppen weiss sind, mit schwarzen 
Domen. 
“ Mit dem Bedauern, dass ich liber Ihre Ansicbten in Betreff der goldigen Puppen, 
die mir sehr annehmbar scheinen, so gut wie nichts aus eigener Erfahrung sagen 
kann, &c .’’ 
The use of the gilded appearance as a warning in Mechanitis seems to be very 
clear, and the fact that the pupae hang in companies must of course greatly add to 
the effect, and this is probably the meaning of the habit (so common, for this reason, 
among many distasteful and conspicuous larvae). It seems probable that the gilded 
spots of Adelpha are instances of persistence with protective value among changed 
surroundings and withdrawal from the substance originally imitated. From Dr. 
Muller’s letter it is quite clear that the resemblance to mineral substances cannot be 
of any protective importance in the Brazilian forests, but it does not therefore follow 
that such surroundings would not intensify the appearance even now. Thus 
V. urticcR in England has been shown to be rendered very brilliant by gilt surround¬ 
ings, although in nature it can rarely receive such a stimulus, and the amount of 
gilding on it is very small or entirely absent. It is satisfactory that Dr. Muller 
should consider my suggestion a probable one as to the biological significance of the 
gilded appearance. 
My friend and pupil, Mr. E. A. Minchin, who has collected insects and observed 
very keenly in India for many years, informs me that the pupa of Euplcea core is 
exceedingly conspicuous, being covered with a brilliant metallic silvery appearance, and 
hanging from its food-plant in such a manner that it can be seen at a great distance. 
As the butterfly is exceedingly common, and is known to be protected by disagreeable 
properties, it is almost certain that the metallic appearance of the pupa acts as a 
warning. This, however, was the only instance of the use of this colour for such a 
purpose which had come under the observation of Mr. Minchin. 
In conclusion, the balance of evidence given by experiment and observation is, I 
think, in favour of the view that the metallic appearance was originally of protective 
value from its resemblance to glittering minerals; that it has preserved its original 
significance amid change of surroundings ; while in other cases it has come to be used 
for an entirely different purpose to render distasteful forms conspicuous. 
Experiments upon Papilio machaon. 
I received 11 almost mature larvae from Mr. W. H. Harwood, of Colchester, on 
August 24,. 1886. The following experiments were made. The eight largest larvae 
