LAMELLAR SYSTEMS 149 



ular material (Fig. 19) which gradually infiltrates the entire matrix 

 and finally separates out into these highly ordered structures. The 

 intermediate stages are surrounded by multiple membranes which 

 are gradually lost. These transition stages demonstrate how a lamel- 

 lar structure can transform into a more highly ordered paracrystal- 

 hne system by a gradual process of condensation. Correlative bio- 

 chemical studies of the paracrystalline granular components would 



Fig. 21. Paracrystalline granule from pigment epithelium of guinea-pig 

 retina, showing regular line or cross-grating pattern of the dense particles, 

 depending on their orientation in the plane of sectioning. Osmium-cryofixation 

 preparation. X 400,000. 



be of interest in view of the studies carried out by Wald and co- 

 workers (Wald, 1958) which emphasize the active contribution of 

 the pigment epithelium in the visual processes. The described para- 

 crystalline components bear a strong resemblance to the protein 

 crystals in the eggs of Limnea stagnalis described by Elbers ( 1957) ; 

 and to the vitelline bodies in the eggs of Planorbis corneus. The 

 high contrast in the macromolecular constituents of these protein 

 crystals with a similar periodicity of 60 A is attributed to the iron 

 content. Of particular interest are the numerous transition forms 



