224 THE ANIMAL KINGDOM. 



RHINOCEROS HORN. 



A section of this beautiful and familiar object is a good 

 example of the effect of polarized light. By common light 

 we see a pale yellowish substance composed of horny fibres 

 interlacing and forming cells of concentric layers round a 

 minute central point. All this is faintly visible ; but sub- 

 jected to the action of polarized light, brilliant bands of 

 gold mark out the compartments, whilst the layers of blue, 

 purple, or green, circle round a spot which probably cor- 

 responds to the papillae of the cutis. 



WHALEBONE. 



A longitudinal section exhibits the laminae of com- 

 pressed cells on either side of the medullary cells, varied 

 and beautiful in colour. The transverse section shows the 

 large concentric cells and pigment granules yet more vividly 

 bright. 



ELYTRA OF DYTICUS. 



This exquisite preparation for the polariscope requires 

 considerable time and care to give it the necessary trans- 

 parency, for the exhibition of colour entirely depends upon 

 the preparation. 



The elytra is naturally hard, black, ribbed, and dotted ; 

 the structure scarcely visible. It must be soaked in potash 

 for a month, then examined, washed, dried, soaked in tur- 

 pentine, and finally mounted in balsam ; when nothing but 

 the suckers of that same beetle can exceed it in colour. 

 The richness of the golden ground, the blue and crimson 

 spots on which the black cross of polarized light is seen, 

 makes it a truly glorious object. 



Hairs from the leaf of a fern show like glittering stars in 

 the dark blue, midnight sky. 



THE CUTICLE OF DEUTZIA LEAF 



shows the stellate siliceous hairs of all colours on the cel- 

 lular tissue. 



