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CONTBIBUTIONS to the OHEMISTEY of INSECT COLOUKS. 

 By F. H. Perky Coste, F.C.S. 

 /w= / 3 II. — A priori Anticipations. 



It will perhaps conduce to clearness if I now quote briefly a 

 few extracts from the notes that I drew up for my own guidance 

 before commencing these experiments. They are not without a 

 moral — seen in the light of later and experimental knowledge ; 

 and, anyhow, my readers will thus be travelling along the same 

 route that I myself pursued. 



Now the results that I anticipated were to have a twofold signi- 

 ficance, viz., from the phylogenetic and the chemical standpoints. 

 Phylogenetically, I anticipated finding illustrations of the evolu- 

 tionary doctrine of the origin of species, and of the various stages 

 represented by each species in a natural group or genus, — at 

 least so far as regards colouring, — just similarly, for instance, as 

 Weissmann found in the markings of Sphinx larva?.* Further- 

 more, I expected to obtain two wholly different lines of results 

 with these colours, according to the nature of the reagents used. 

 I anticipated obtaining (a) progressive, and (b) retrogressive, modi- 

 fications ; and it also seemed possible that by such results some 

 light might be thrown on classification. And, lastly, similar 

 markings in different colours on allied species might be expected 

 to yield a common colour (either progressively or retrogressively) 

 under the influence of the same reagent. 



Chemically, I hoped to compile a table of the colours in their 

 biological rank, and noted it as very interesting, when the appa- 

 rently same colour occurred in different groups, to determine 

 whether it would be affected in the same way (c/., for instance, 

 the yellow of the under wing in the Triphsense and in Heliaca 

 arbuti). Only after writing the above did I recollect that Grant 

 Allen (reasoning, however, not from the results of experiments, but 

 from observation alone) had drawn up a table of colours, in their 

 biological rank, for flowers ; and it struck me as very interesting 

 to see how far my results might accord with his. I expected that 

 in insects yellow would be found above white {not below, as in 

 flowers), and below red. But what of black (probably above all 

 these), blue, brown, &c. ? That remained for experiment to show. 



Nevertheless, I wrote, — very likely a linear arrangement of 

 all the colours may be impossible ; for as to the ranks of colours, 

 I doubt if there be a universal unity ; but rather suspect that a 

 colour may rank below a second colour in one group, and above 

 it in another. I imagine this to be the case from a consideration 

 of the distribution of colour on various insects ; broadly speaking, 



* ' Essays in Descent ' (Meldola's translation), I., 223, &c. 



