146 



MACROMOLECULAR COMPLEXES 



with a dense layer approximately 60 A thick. In dark-adapted insect 

 eyes, a dense, granular component with indications of orientation is 

 seen in the outer tubular compartments, particularly after platinic 

 chloride-osmium cryofixation. Continuation of these studies, which 

 have already demonstrated characteristic differences between dark- 

 and light-adapted photoreceptor elements, will undoubtedly prove 

 to be of interest in connection with the postulated models of photo- 

 receptor structure (Wald, 1958; Wolken, 1958b). 



Paracrystalline Components of the Retinal Pigment Epithe- 

 lium. The pigment epithelium is intimately associated both struc- 

 turally and functionally with the photoreceptor elements of the 

 vertebrate retina (Wald, 1958). Previous electron microscope 

 studies (Porter, 1957; Yamada et ah, 1958) had demonstrated the 

 presence of characteristic lamellated components in the cytoplasm 

 of the pigment epithelium cells. With improved preparation tech- 

 niques, it has now been possible to resolve the highly regular, para- 



Fig. 18. Dense granules and modified mitochondria in pigment epithelium 

 of guinea-pig retina. Certain forms of these granules are surrounded by multiple 

 membranes (arrow) and show no distinct internal fme-structure in standard 

 preparations. Osmium fixation-araldite embedding. X30,000. 



