88 ON THE VARIATION OF SPECIES. 



the group is one of those wherein great changes seem to he 

 now going on. A conspicuous member of the group is the 

 H. Melpoynene of Linnaeus. This elegant form is found 

 throughout Guiana, Venezuela and some parts of New Gra- 

 nada. It is very common at Obydos, and reappears on the 

 south side of the river in the dry forests behind Santarem, 

 at the mouth of the Tapajos. In all other parts of the 

 Amazons valley, eastward to Para and westward to Peru, it 

 is entirely absent. This absence at first appeared to me very 

 strange ; for the local conditions of these regions did not 

 appear so strongly contrasted as to check, in this abrupt 

 manner, the range of so prolific a species ; especially as at 

 Obydos and Santarem it occurred in moist woods close to the 

 edge of the river. Another and nearly allied species, how- 

 ever, takes its place in the forest plains, namely, the H. 

 Tlitlxiope of Hiibner. This is of the same size and shape as 

 its sister kind, but differs very strikingly in colours : H. 3Iel- 

 poniene being simply black with a large crimson spot on 

 its wings, whilst H. Thelxiope has these beautifully rayed 

 with black and crimson, and is further adorned with a num- 

 ber of bright yellow spots. Both have the same habits. 

 H. Melpomene ornaments the sandy alleys in the forests of 

 Obydos, floating lazily in great numbers over the lower 

 trees ; whilst H. Thelxiope, in a similar manner and in 

 equal numbers, adorns the moister forests which constitute 

 its domain. No one who has studied the group has doubted 

 for a moment that the two are perfectly and originally 

 distinct species, like the hare and rabbit, for instance, or any 

 other two allied species of one and the same genus. 



The following facts, however, led me to conclude that the 

 one is simply a modification of the other. There are, as 

 might be supposed, districts of forest intermediate in cha- 

 racter between the drier areas of Obydos, &c. and the moister 



