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1. 1. By permeabilizing entire retinae with the saponin β-escin and then loading the photoreceptor cells of the crayfish Orconectes limosus with oxalate and ATP, we localized calcium-accumulating organelles. The Ca-oxalate-deposits were identified with the electron microscope. 2. 2. The photoreceptor cells of crayfish contain three kinds of calcium-accumulating organelles: submicrovillar cisternae, mitochondriae and electron dense pigment granules. 3. 3. The submicrovillar cisternae appear tubelike and are less voluminous than those of other arthropods. 4. 4. The deposits found in the pigment granules support the hypothesis that they are involved in calcium regulation. 5. 5. The effect of β-escin on the electroretinogram was also tested. β-Escin causes a diminution in the ERG-amplitude which stays stable for 1 hr.

1. 1. Endogenous peroxidase was localized by electron microscopy within the retinal tissue of the golden Syrian hamster. 2. 2. Peroxidase activity was found in the apical parts of rod outer segments, in the cytoplasm and phagosomes of the retinal pigment epithelium (RPE), and extracellularly between the basal infoldings of the RPE. 3. 3. No reaction product was detected when either H 2 O 2 or tetramethyl benzidine were omitted from the reaction medium. 4. 4. The same was true when the tissue was osmicated before the incubation in the reaction medium or treated with 100 mM sodium azide. 5. 5. These results indicate that the peroxidative activity was enzymatically mediated.

1. 1. Rhabdomeral microvilli of photoreceptor cells of invertebrates contain a labile central cytoskeleton. For stabilization of the rhabdomeral cytoskeleton of the crayfish Orconectes limosus the crosslinking reagent suberic acid bis (N-hydroxysuccinimide ester) was used. 2. 2. It was found that this crosslinking reagent can be successfully used to stabilize and isolate the microvillar cytoskeleton of crayfish photoreceptors. 3. 3. After detergent treatment cytosolic proteins and the cell membranes were removed. 4. 4. By the combined use of crosslinker and detergent the accessibility of antibodies or other markers to the microvillar cytoskeleton is possible. 5. 5. This method may be useful, because at present little is known about the proteins associated with the central filament of invertebrate photoreceptors.