26o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



SUMMARY 



1. The elongated molecular chains of arthropodin are oriented per- 

 pendicular to the chitin chains in normal insect cuticle. The result 

 is a cross-grid arrangement (figs. 2 B-D, 3) with both protein chains 

 and chitin chains parallel to the cuticle surface. 



2. The optical properties of cuticle are at least approximately an 

 arithmetic sum of the optical properties of the component chitin and 

 arthropodin chains. 



3. Extracted arthropodin has a refractive index of about 1.554. 

 In aqueous solution it consists of particles large enough to produce a 

 Tyndall effect and elongated enough to show flow birefringence. 

 Drawn fibers are also birefringent. The birefringence is positive rela- 

 tive to the long axis of the particles and is at least largely a form 

 birefringence. 



4. Values for the magnitude of birefringence were determined as : 

 Cuticle = 0.00070, chitin = 0.00084, ^Lnd arthropodin = 0.00013. 



5. The impermeability of dried cuticle is due to the arthropodin, 



6. The influence of these findings on current concepts of cuticle 

 organization is discussed. The data do seem to rationalize the failure 

 to find microfibers in electron-microscope pictures of normal insect 

 cuticle. 



LITERATURE CITED 



Bear, R. S., and Sen mitt, F. O. 



1936. The measurement of small retardations with the polarizing micro- 

 scope. Journ. Opt. Soc. Amer., vol. 26, pp. 363-364. 

 Castle, E. S. 



1936. The double refraction of chitin. Journ. Gen. Physiol., vol. 19, pp. 797- 

 805. 

 Dainty, M. ; Kleinzeller, A.; Lawrence, A. S. C. ; Miall, M. ; Needham, J.; 

 Needham, D. M. ; and Shen, S. C. 



1944. Studies on the anomalous viscosity and flow birefringence of protein. 

 Journ. Gen. Physiol., vol. 27, pp. 355-399. 

 Dennell, R., and Malek, S. R. A. 



1956. The cuticle of the cockroach PcripJancta amcricana. VI. The com- 



position of the cuticle as determined by quantitative analysis. Proc. 

 Roy. Soc. London, ser. B, vol. 145, pp. 249-258. 

 Duchateau, G., and Florkin, M. 



1954. Sur la composition de I'arthropodine et de la scleroproteine cuticu- 

 laires de deux crustaces decapodes {Homarus vulgaris Edwards, 

 CalUncctcs sapidns Rathbun). Physiol. Comp. et Oecol., vol. 3, 



pp. 365-369- 

 Foster, A. B., and Hackman, R. H. 



1957. Application of ethylenediaminetetra-acetic acid in the isolation of 



crustacean chitin. Nature, vol. 180, pp. 40-41. 



