THE VERTEBRATA 159 



tallic " lustre, may be produced by means of 

 pigment, in the vegetable as well as in the 

 animal organism ; for instance, in the dark 

 centres of Coreopsis (the Beetle Flower), and 

 several other fashionable garden plants be- 

 longing to the Compositse or Daisy family. 

 Within the animal kingdom, we may note that 

 the metallic lustre is almost entirely confined 

 to land animals ; their dry skins have more 

 chance to develop opaque parts, than the moist 

 tissues of creatures that live in the water. The 

 most familiar exception to this rule is the Sea- 

 Mouse, an Annelid worm found on English coasts 

 (P- 73)> which receives its odd name because it 

 is a fat oval creature, covered with bristles, thus 

 greatly differing in appearance from most worms. 

 The larger bristles, which are of a dark purplish- 

 black colour, have a bronze or golden metallic 

 lustre. Various other annelids exhibit brilliant 

 rainbow colours ; for example, Nereis, the Rain- 

 bow Worm, also found on English shores; but 

 without the underlying black opaque pigment, 

 the reflections from the surface fall short of 

 absolutely metallic brightness. On land, we see 

 among the insects innumerable forms which pre- 

 sent a metallic lustre, the beetles being the most- 

 notable in this respect. To return to the verte.- 

 brates, from which we started, everybody must 

 have noticed that the fur of a clean well-kept 

 black cat, when lit up by the bright sunlight in 

 which the animal loves to bask, shows little 

 rainbow reflections of red and green. These 

 are due to the presence of little grooves and 

 irregularities on the surface of the hairs, which 

 play the same part in breaking up the light 

 which they reflect, as do the sharp angles of 



