514 Mr. G. Lewis' supplementary note on the 



ments of the birds, and these feathers are very beautiful. 

 In the humming-bird, Orcotrochilus picJmicha, the 

 feathers of the breast are fihform and non-metallic, but in 

 Topaza piza the whole breast is clothed with lamelliform 

 feathers, and it is highly metallic. In Amazilis the 

 feathers on the rump are laminated and metallic. In 

 others there is another form of feather, a feather, 

 in fact, of filiform structure, which has commenced to 

 be flattened out ; here there is metallic lustre, but not 

 the brilliancy of the short lamelliform feather. How far 

 light may be the factor in creating the general form of 

 the feather is a matter of the greatest interest, for it is 

 significant that in birds it requires a lamelliform feather 

 and in butterflies a surface free of hair or down before 

 great brilliancy appears. White birds and white animals 

 belong, generally speaking, to the temperate and northern 

 zones, and the whiteness of a swan may arise from the 

 structural benefit attending that whiteness. The oily 

 substance on the feathers which enables aquatic birds 

 to rest in the water may receive the impressions from the 

 rays, and thus prevent them from becoming permanent 

 on the feathers. Perhaps there is a special absence of 

 this oil on the metallic feathers of the mandarin duck. 

 The swan has the habit of putting his whole neck and 

 head under water, but I doubt if this is so much the 

 habit of the duck tribe when there is brilliant plumage 

 on the head and neck. A laminated feather could not 

 retain oil. 



I do not like to refer to tame birds, but the rock pigeon 

 is close to our domestic one, so I take the last as another 

 example. Pigeons strut about the ground picking up 

 grain, moving the head and neck-feathers with a quick 

 undulatory movement, which is almost incessant. The 

 head and neck-feathers meet sun-rays at every angle, 

 and the beautiful tints are diffused, not localised as in 

 the humming-birds. 



It is almost a relief to turn from the contemplation of 

 these exquisite structures in birds and butterflies to think 

 of the bark of a cork-tree, or the even rougher hide of 

 a rhinoceros. But in turning round sharply, we see the 

 more clearly, that sun-rays cannot materially affect rude 

 structures like these ; and we miss at once what we call 

 beauty of colour. And what do we learn ? We see that 

 when Nature has provided the surfaces on which solar- 

 rays can act, metallic brilliancy must come, for it is 

 simply a matter of structure. 



