THE INTEGUMENT 11 



or water once more, and so increases its bulk before its cuticle has 

 hardened. 



Metallic colours of the cuticle 



In many insects the surface of the cuticle itself, or of the flattened 

 scales which are articulated to it, show brilliant metallic colours. la 

 most cases these colours result from some periodic structure in the 

 cuticle. In at least one insect, the beetle Serica sericea, the faint iri- 

 descence is due to diffraction by fine striae: collodion impressions of 

 the wing, bearing a cast of this structure, show the same iridescence 

 as the wing itself. But in the majority of cases iridescence is the 

 result of interference by multiple thin films separated by material of 

 slightly different refractive index. Horizontal thin plates of this kind 

 are responsible for the metallic colours of Lycaenids and many other 

 butterflies. The brilliant blue of Morpho butterflies is produced by 

 thin plates which are inclined at an angle to make up the glassy ridges 

 that run lengthways along the scales. These periodic structures pre- 

 sumably arise spontaneously by crystallization within the structure 

 of the cuticle: ordinary Lepidopterous scales show periodic pro- 

 jections apparently homologous with those which produce the 

 colours in Morpho. 



BIBLIOGRAPHY 



andersen, s. o. and weis-fogh, t. Adv. Ins. Physiol., 2, (1964), 1-66 (the 

 rubber-like protein 'resilin' of insect cuticle) 



beament, J. w. l. Biol. Rev., 36, (1961), 281-320 (water relations in insect 

 cuticle: review) 



cottrell, c. b. Adv. Ins. Physiol., 2, (1965), 175-218 (hardening of insect 

 cuticle: review) 



hackman, r. h. Physiology of Insect a, III. (Morris Rockstein, Ed.) Aca- 

 demic Press, New York, 1964, 471-506 (chemistry of insect cuticle) 



locke, m. Physiology of Insecta, III. (Morris Rockstein, Ed.), Academic 

 Press, New York, 1964, 379^70 (structure of insect cuticle) 



Richards, A. G. The Integument of Arthropods, Minneapolis, 1951 



rudall, k. M. Adv. Ins. Physiol., 1 (1963), 257-313 (chitin-protein com- 

 plexes in cuticle) 



wigglesworth, v. b. Ann. Rev. Entom., 2, (1957), 37-54 (physiology of 

 insect cuticle : review) 



The Principles of Insect Physiology, 6th Edn., Methuen, London, 



1965, 25-63 (insect integument: properties, formation and shedding 

 of the cuticle) 



