518 Mr. G. Lewis' supplementary note on the 



catch these rays in a greater degree than others. In the 

 humming-hircl it is the head, throat, &c. ; in the butterfly, 

 the expanse of wing ; the one has feathers and the other 

 scales, and these are both of that substance which 

 enables them to take impressions from the sun. The 

 light, direct waves from the sun are the most subtle and 

 delicate of all solar-rays, and produce the finest ribs. 

 Spots and ocelli in Lepidoptera seem to me raised 

 places and depressions in the wings, or are sometimes 

 owing to the different make of scales in those parts. 

 The lamelliform feather of a humming-bird is not very 

 different to the surface presented to the sun in the wing- 

 case of a Buprestis. 



Opacity of substance is almost universal in the bodies 

 of terrestrial animals and plants, but I will mention two 

 instances of pellucidity. First, the blind Rhyncophora, 

 discovered within recent years under stones in the South 

 of Europe, Raymondia, Alaocyha, TroglorrhyncJius, &c. ; 

 and, second, ferns of the Hymenophyllum group. The 

 first live in perhaps absolute darkness, and are never 

 touched during life by light-rays ; the second are only 

 subpellucid, and live in the shadiest parts of forests, 

 where they are subject to indirect rays. Cave insects, 

 such as Trechus and Polystichus, are testaceous, and seem 

 to me to be on the road to pellucidity, but have not yet 

 had time to assume it. If we knew nothing of the laws 

 of light, it would perhaps be natural to look for a 

 general tendency to transparency where the sun's rays 

 are least obstructed, but in reality we must for this turn 

 to aquatics, and look into a pond ; there we see numerous 

 examples of it. The larvae of Neuroptera and Libellulce, 

 shrimps and fishes, are pellucid, because light-rays are 

 diverted from them by refraction, for light glances off 

 sideways on touching the water, and the ribbed structure 

 essential for colour is, generally speaking, absent in these 

 animals. The fish, however, which would feed on the 

 transparent larvae have eyes formed to see their outlines 

 and movements in the water, just as they have a tail 

 and fins for swimming, and pellucidity in aquatic larvae 

 is not protective any more than the greenness in the 

 case of Daphnis nerii. Light also moves faster in the 

 air than water, so that even if rays acted directly on 

 the integuments of the shrimps, the effect would be less 

 powerful. 



The sooner we sift thoroughly the protective colour 



