XIII 



observations made upon Allotinus Horsfieldi Moore, and referred to in the 

 special discussion of this species, gives us reason to believe that this is 

 connected with their mode of life. In the same way it is not unlikely that, 

 while Lycaenidae in general are very fond of the sun, the butterflies of this group, 

 like many Satyridae, prefer a half darkness ; the brilliant colouring so characte- 

 ristic of the Lycaenidae, is not found in this group, they are more brown and 

 grey in colour, and it is not improbable as we shall show later, that a strong 

 development of the structural colours is connected with strong light. The 

 Miletus Symethus Cram, found in Java is accordingly grey or brownish, on 

 the upperside in particular dark brown, but there is also on the upperside 

 of the primaries sometimes a great deal of white, usually, however, only in 

 the female. It occurs occasionally in a male, but in these it is usually covered 

 by a dark pigment, in very varying degree in different individuals, so that 

 some differ very little from the female, while in others the white remains only 

 as a small spot; and between these two extremes it is found in less and 

 greater degrees. If a number of butterflies of this last kind are inspected, it 

 becomes plain that the white upon the upperside is in a state of change, 

 which in some individuals is just beginning, in others has proceeded further, 

 while in yet others it is very far advanced. A process which always follows 

 exactly the same line of development. The question then arises, whether this 

 process consists in a gradual increase of white, or on the contrary in an increase 

 of the dark pigment such as to cause a gradual decrease of the white? In 

 which of these two directions is the process moving? At first sight one seems 

 as likely as the other. The butterflies of this species, in proportion as the 

 process is advanced, appear as a series, in which at the one extreme white 

 is most, and at the other least prepronderating. In the female white takes up 

 not only a large part of the upperside of the primaries, but is found on the 

 same side of the secondaries, here differing in extent in different individuals, 

 and often assuming the elongated from that indicates the encroachment of the 

 surrounding darker pigment, which ultimately must lead to a narrow relic 

 stripe only being left. And this we actually find upon the upperside of the 

 secondaries of many males of this species, in a faint white stripe partially covered 

 by the darker scales, thereby demonstrating that the evolutionary process in 

 this case consists in an increase of the darker pigment, which gradually covers 

 over the white. The most advanced condition is, therefore, found in the males, in 

 whom the white has been reduced to a small remnant. (See Plate XIX ?>b,c,d,e,/). 

 This is further confirmed by a similar relic stripe that is found in Allotinus 

 Horsfieldi Moore, (PI. XIX, i2a,b, 14a) A. Portunus, de Nic. (PI. XX, 18^) 

 and some other species of the related Gerydinae-genus Allotinus Felder, in 



