INSECT CUTICLE — RICHARDS AND PIPA 



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have failed to detect microfibers by electron microscopy in normal 

 insect cuticle (Richards, 1958). Microfibers become visible in the 

 electron microscope after treatments which disrupt or remove the pro- 

 tein. Aggregates that presumably represent chitin micelles (pi. 2, 

 fig. i) and seem to align (pi. 2, fig. 2) to give microfibers which in 

 turn associate into larger fibers (pi. 2, figs. 3, 4) have been treated in 



'b' 



Fig. 3. — Three-dimensional reconstruction of cuticle lattice with a, b, and c 

 axes indicated. Chitin chains drawn as irregularly displaced cylinders, the 

 arthropodin chains as rectangular bodies with side groups of various sizes. 



some detail by Richards (1955). One would expect the aggregates 

 and small microfibers to be more or less masked by cross-bonding 

 protein chains. Such a masking effect should become less with increas- 

 ing fiber size. Accordingly, one should not be surprised to observe the 

 large fibers called "Balken" in normal cuticle and yet fail to find the 

 small microfibers until their contrast is augmented by protein re- 

 moval. At present, however, this is only a logically satisfying guess — 

 whether or not it is true remains to be proved. 



The more gross aspects of cuticle organization, notably the micro- 

 scopically visible laminar structure, can only be speculated about at 

 present. It seems quite reasonable to suppose that these originate 

 from competitive depositions (Picken, 1949) or from energy troughs 

 in electrostatic fields (Richards, 1951), but data simply do not exist 

 for making any objective choice among conceivable mechanisms. 



