﻿158 THE ENTOMOLOGIST. 



could first turn its black into yellow, and then the yellow to 

 white ; although, I should add, that in this particular case I 

 fancied the black had never come through yellow at all, but 

 direct from the Pieris black, and that from white ; but, at any 

 rate, in such an instance as that of G. cleopatra and G, rhamni, 

 I hoped to reduce the red flush and spots, respectively displayed 

 by them, to the ground yellow, and then this yellow to the type 

 colour of the genus, as shown by the lowest forms. Again, in 

 species displaying so many colours as the Vanessse do, it would 

 be most interesting to find the lineal order of these, although, no 

 doubt, some would be collateral, and not all unilineal. 



Then, again, regarding the statement I have already quoted 

 (p. 155, above), that the same markings differently coloured in 

 allied species might be expected to yield a common colour on 

 treatment with retrogressive reagents, it appeared to me that a 

 crucial instance would be afforded by the species of Catocala, 

 e.g., nupta and fraxini. Was the blue of fraxini, I asked, evolved 

 via the red of nupta (or vice versa), or are not these two colours 

 more probably collaterally divergent ? In the first case one 

 might expect this result -.—fraxini, blue reduces to red : this to 

 "x" nupta, red reduces to "%" ; but in the second case, both the 

 blue of fraxini and the red of nupta might be reduced by a 

 common reagent (or by different reagents) to a common colour. 

 An analogous instance to that of these Catocalse is afforded by 

 the two species, Euchloe cardamines and E. eupheno, in which 

 latter the ground colour is bright yellow, and the tip orange. 

 By thus applying this principle to all genera that display the 

 same markings in different colours, I hoped to discover the 

 actual order of coloric evolution in each species, and the genetic 

 relationship to all the others. 



Such were my expectations as regards retrogressive reagents. 

 It will appear that they have been only partly realised, since I have 

 not succeeded in destrojdng highly evolved colours, step by step, 

 but have never obtained more than one retrogressive change. 



That the above-stated opinions maybe viewed in their proper 

 light, I must again remind my readers that I have simply been 

 quoting to them from notes written out before I had made a 

 single experiment. I trust that I have not been unduly prolix in 

 so doing, but it seemed to me that greater coherence and unity 

 would thus be given to my paper than could obtain, did I omit all 

 reference to my previous anticipations, and plunge directly into 

 the experimental results. Moreover, the speculations I had 

 indulged in of obtaining those progressive modifications appear 

 to me to carry a moral and a warning, only illustrating once 

 more the utter futility of relying on an}*- a priori hypothetical 

 views, — however probable they may seem, — without subjecting 

 them to the test of experiment. Hypotheses certainly are 



