Regional morphological variations within the crayfish eye.

The existence of structural asymmetries has been quantitatively demonstrated in the crayfish compound eye. Variations in the size of the rhabdomes and corneal facets, as well as the size and extent of the accessory reflecting pigment cells, have been found. It was determined that the mean rhabdome diameter within a 70 degrees arc in the dorsal quadrant of the retina is 11-19% smaller than the mean rhabdome diameter in the remaining areas of the eye. Also, the extent of the accessory reflecting pigment cells is diminished over an area corresponding generally to the dorsal region of smaller rhabdomes. Corneal facet size and shape vary over the surface of the cornea, with smaller facets occurring in the dorsal region. Both the mean rhabdome diameter and the mean corneal facet area for whole eyes increases linearly in animals ranging in size from 3.9-12 cm. The estimated number of corneal facets, and therefore the number of rhabdomes, increases from an average of 4700 in the 3-6.9 cm size range to about 6000 in 7-12 cm animals. These data indicate that structural asymmetries and various size-related parameters exist in the crayfish eye and should be considered in any quantitative analysis of this structure.