X INTRODUCTION. 



a direct development of yellow, leading up to the brown in typical Cceno- 

 nympha pamphilus, C. davus &c. Under the action of ammonia, the 

 pale undersides and fringes of these species become very yellow and 

 lead insensibly into the normal brown coloration. It would seem, 

 therefore, that the general action of alkalies, in this direction, is to 

 develop progressive coloration white (pigmented) to yellow, and 

 yellow to red, whilst Mr. Coverdale wrote in 1886, that " a great many 

 acids (hydrochloric, nitric, sulphuric &c.), restored the pigment, when 

 thus changed, to its natural colour." Whilst dealing with this relation 

 of brown and yellow, I would notice, that the dark brown edging to 

 the anterior wings of Epinephele tithonus, Cwnonympha pamphilus var. 

 lyllus, and their allies, is much more readily acted on than is the orange 

 colour in this species, which is rather remarkable when the colours are 

 considered in their genetic relationship but is not at all so from a 

 varietal point of view. The unstable character of this band is very 

 marked, and only occurs occasionally in certain varieties of some 

 species although it is quite constant in others. Here then, we notice 

 that a colour in a condition of transition or formation, may be, and 

 probably is, more unstable than the colour from which it springs, 

 although the latter, genetically considered, is of course lower than the 

 former. Such a case, is found in Callimorpha hera, the red form of 

 which is changeable readily to yellow, the normal colour of its var. 

 lutescens, and, at the same time, is itself rather more readily reduced 

 completely to white than is the yellow variety before mentioned. The 

 dark brown of Thanaos tages is of the same unstable character, and it is 

 probably quite a recent offshoot from the more yellow brown of its allies 

 in the genus Hesperia. The transitional and unstable character of the 

 darker colour in Epinephele and its allies, gives a decided proof of their 

 probable recent development. The brown found in those varieties of 

 Angerona prunaria in which the bright orange is reduced to a small 

 patch in the central area of the wing, is also of a very unstable nature 

 and easily affected ; not so the orange which is particularly stable. I 

 had often wondered what was the cause of the peculiar glossy appear- 

 ance noticed in some species such as Satyrus semele, but have proved that 

 this is superficial and not due to the normal pigment, as it remains after 

 all the pigment is artificially bleached from the wing. 



Eut of the direct retrogression of red and brown forms to 

 yellow, we have numerous examples. There are yellow varieties of 

 Arctia caia, Callimorpha her a, C. dominula, Zygoma filipendulce, Z. trifolii, 

 Z. lonicerce, all tending to show retrogressive development. Cases of 

 Catocala nupta with the hind wings also partially yellow are of the 

 same kind. I consider that brown and red are essentially only one 

 colour, and hence we find in another direction, that the yellow tends 

 to brown. It follows, therefore, that normally brown species will 

 have yellow varieties, and vice versa if the tendency of the coloration 

 is in that direction. No species appears to illustrate this so well as the 

 common sexually dimorphic Odonestis potatoria. The $ 's of this 

 species may for convenience be called yellow, whilst the more highly 

 developed males are brown, but I have in my cabinet a brown female 

 and a yellow male, and there are many others on record, and both the 

 yellow and brown readily fade to white. Following out the develop- 

 ment in this direction we find that Bombyx quercus offers a similar and 

 parallel instance, the females again being yellow, but the males of a 



