192 THE ENTOMOLOGIST. 



varieties of caia (Entom. xxiii. 239, 259), Sesia with yellow bands 

 instead of red (Entom. xxii. 192). It is again evident that such 

 varieties are identical with those that may be obtained by the 

 action of acids on the normal red species. 



F. Interchange of red and green. * This is an exceedingly 

 interesting, but very difficult variation. We may obtain some 

 collateral evidence by comparing the normal colouring of the two 

 sexes ; for instance, Wallace states that in many S. American 

 Papilios the green spots on the male are represented by red on 

 the female.f There is a variety of M. margaritaria chronicled in 

 which the cilia are red ; this may be a case in point, and 

 some further information may perhaps be gained from the con- 

 sideration of an extraordinary variety of A. galathea, to which I 

 must presently refer. This is emphatically a subject in which far 

 more information is wanted. 



Then as to progressive pigmental variation, I have already 

 given a few instances of yellow and orange varieties of normally 

 white species. I greatly regret, however, to have found no 

 records of any red varieties of yellow species ; such varieties 

 would be highly interesting — of great theoretical importance — 

 especially if tbey occurred in species belonging to a genus that 

 already comprised red forms. 



Now for the extraordinary variation of Arge galathea, already 

 referred to. It is stated (I presume on good authority) that a 

 specimen is known marked with green and red. For a long time 

 this seemed utterly unintelligible and inexplicable to me, but I 

 now think it an interesting confirmation of my views. Clearly — 

 after what has been stated in preceding sections — it would be 

 nothing remarkable to find a yellow variety of A. galathea; now, 

 in the red and green variety, it would seem that, owing to some 

 altogether exceptional metabolic conditions, not only has a yellow 

 pigment been developed, but that this has advanced at one bound 

 to its consummation in red, and also simultaneously to its other 

 and divergent goal — green. It is therefore a highly interesting 

 phenomenon, and one in which more information is certainly 

 desirable. 



[We must defer the conclusion until September. — Ed.] 



* Wallace remarks, in 'Tropical Nature' (p. 134), that the change from green 

 to red — from the more refrangible to the less refrangible is in accordance with the 

 law of change which has been shown to accompany expansion (i. e., by heat) is 

 Inorganic — growth and development in organic — forms. The reference here is to 

 a series of experiments by Mr. Ackroyd, detailed in the ' Chemical News ' for 

 August, 1876, where it is shown that the effect of heat on a large number of 

 chemical compounds is to change the colours from a more to a less refrangible 

 colour. With all respect to Dr. Wallace, I must say that the comparison which he 

 attempts to institute between these phenomena of metachromatism and the de- 

 velopment of organic colours is, to say the least of it, forced. Moreover, as a 

 matter of fact, I have now shown that there is at least some reason to believe that 

 green was developed from yellow, in which case we have yellow developing, on the 

 one hand, into the more refrangible green, on the other, into the less refrangible red. 



t ' Tropical Nature,' 178. 



