Post-embryonic development of the lateral eye of Cloeon sp, (Ephemeroptera: Baetidae) as revealed by scanning electron microscopy

Post-embryonic developmental patterns of the lateral eyes of both male and female Cloeon sp, are described and compared with each other morphometrical ly on the basis of scanning electron microscopy. In the larvae number of om matidia, ommatidial size, and total corneal surface area of the eye increas e towards the subimaginal moult. It is then that clear differences between males and females begin to occur: while further increases in the number of ommatidia are recorded from the lateral eye of subimago and image females ( accompanied by decreasing facet sizes and interommatidial angles), males sh ow decreasing numbers of ommatidia and total corneal areas in their lateral eyes as they prepare to leave the water. Consequently, the lateral eyes of a female are larger than those of a male image. It appears that the enormo us development of the dorsal eyes of the males has occurred at the expense of the lateral eyes. In male as well as female lateral eyes two major facet shapes are encountered: squares with rounded corners which are predominant ly found in the central and upward looking areas, and hexagons which are do minating the lateral and ventral-facing regions. The different roles of the lateral eyes in male and female baetid mayflies is discussed in relation t o their flights and the intriguing idea is presented that females might cho ose males with the largest dorsal eyes.