26 



Applied BiopJiysics 



cuticle and by the lethal symptoms which are coincident with 

 the first visible signs of a reddish-brown tinge in the cuticle. 

 The tanning action of the quinone monomer is also accompanied 

 by the deposition of the colored polymerized oxidation products, 

 and these can be observed in optical sections of the cuticle outer 

 layers. The mosaic structure of the epicuticle in the housefly 

 larva, Miisca domestica, is now shown up clearly 1)y the differ- 

 entiation of the tanned zones from the untanned zones where the 

 lipid is more strongly attached to the protein. The extension of 

 the dimensions of the tanned regions which takes place under 

 the progressive action of chloroform sensitization or kerosene 

 sensitization results in a reduction in the more lipophilic zones, 

 corresponding to the mosaic shown in figure 2b. We may con- 

 clude that the lipid between the discrete aggregates of the mosaic 

 is also more readily displaced from the apparent network in 

 which the lipophilic mosaic is embedded (figures 3a, 3/?, 3c). 



I /OM I 



FIG. 3. Artificial Tanning and Hardening of Insect Cuticle 



(Mitsca domestica). 

 a, h, c Optical section of epicuticle layer, showing progressive tanning by p-henzo- 

 quinone in mosaic network where lipid is displaced by fat-solvent action (dark 

 regions) (nonenzymic). 



d, e, f Similar progressive tanning by catechol (enzymic), 



