118 Mr. G. M. Mathews on the [Ibis, 



species it is deduced that the ancestral coloration was an 

 unmottled green. The nearest approach to this coloration 

 is seen in the species caledonicus, which in the immature has 

 the gVeater part of the plumage of that colour. To follow 

 the explanation hereafter, it had better be recorded that 

 there is a distinct cheek-patch which is usually blue, in 

 some cases blue and white, in others white, and in one case 

 yellow. This is an easy feature to group the species by, and 

 we can note its direct evolution from a non-differentiated 

 cheek, as the immature of caledonicus shows this cheek- 

 patch of quite an undecided blue, partly greenish. The 

 most highly developed species, exiniius, has a white cheek- 

 patch distinct in the young. The yellow-cheeked species is 

 a peculiar one in many respects, showing plasticity and 

 variable adult coloration. It appears to be developing in 

 two phases under the stresses of different Avestern environ- 

 ments from an all-green immature similar to that of 

 caledonicus. We may conclude that the yellow cheeks have 

 developed independently of the blue, though it seems that 

 the white are a later product through the blue. Tiius the 

 northern species have the cheeks mixed white and blue, the 

 white apparently being produced at the expense of the Ijlue. 

 Further, this elimination of blue cheeks is accompanied by 

 an albinistic tendency in one species, but in the other by a 

 complex melanism. Hence we cannot deduce much from 

 the variation of one feature only. However, by the con- 

 sideration of all the features we may arrive at some valuable 

 result, and consequently it is necessary to lay some stress 

 upon apparently trivial points. 



The colour that is present in every species is red, so that 

 we may suggest an erythristic element in the original species, 

 the ancestor of caledonicus. It has predominated in the 

 species elegans, become lessened in flaveoltis, only surviving 

 in the under tail-coverts of the northern species adscitus and 

 venustus; in the species e.ri?/im5 it has developed coincidently 

 with a yellow coloration, while in the western form icterotis 

 it is now in a most interesting stage. Thus the coastal form 

 appears to be mostly green on the back, though the under 

 surface is red in the adult. In the interior the green back 



