Gn Oa) [xci, xcii 
pigmentation and certain external or internal conditions, such 
as horizontal or vertical distribution, season and sex. Can any 
of these conditions be regarded as a direct cause of melanism 2 
“(1) As instances of the influence of horizontal distribution, 
or locality, we have Zronia cleodora as above; Belenois mesen- 
tina of Africa and India with its Australian representative 
B. teutonia, Fabr.; and B. severina, Cram., 9 from Natal 
compared with 2. severina 2 from the Victoria Nyanza. 
‘*(2) As examples of the influence of vertical distribution we 
may take Tutochila autodice, Hiibn., 9 from Buenos Ayres, 
and 7. stigmadice, Stdgr., 2 from the Andes of Ecuador. A 
familiar case of the same kind is the ordinary Ganoris napi, 
Linn., ¢ of Switzerland compared with G. bryonix, Ochs., of 
the high Alps. 
‘*(3) To illustrate seasonal influence we may compare the 
dry- and wet-season forms of Teracolus annex, Wallgrn., 
T. antigone, Boisd., 7’. omphale, Godt., Glutophrissa saba, Fabr., 
Appias libythea, Fabr., Tachyris hippo, Cram., Huphina nadina, 
Lue., H. nerissa, Fabr., and Jxias evippe, Drury. In all these 
the tendency towards melanism in the rains shown by the 
females is well marked. The corresponding males are also 
affected, though in less degree. 
“(4) As exemplifying the influence of sex, we have Delias 
inferna 3 and ° as above, D. descombesi, Boisd., D. eucharis, 
Drury, Zerias tominia, Voll., and 7. zita, Feld. 
“It seems obvious that in all these cases there must be 
some relation or other between the increase of dark pigment 
and the conditions that have been named. But is the bond 
between them one of direct causation? It will be found that 
the attempt to rank any one of these conditions as an actual 
and immediate cause of melanism is attended with great 
difficulty. 
“(1) Melanism cannot be purely a matter of different 
climatic conditions dependent on horizontal distribution, 
because in any given region it often happens that only one 
sex shows a tendency towards melanism, the other sex remain- 
ing unaffected. Moreover, as in the case of Belenois mesentina 
and B. raffrayt, we may have two closely allied butterflies from 
the same locality, one nearly white and the other almost black 
