Ecdysteroids have been found in eyestalk tissues of the fiddler crab, Uca pugilator. Throughout the molt cycle, ecdysteroids are present in much higher concentrations in the eyestalk tissues than can be accounted for by equilibrium diffusion from the hemolymph. The greatest eyestalk-to-hemolymph ratio is found during anecdysis, the nonmolting period when the highest levels of the molt-inhibiting hormone are being produced and released from the eyestalks. RIAactive ecdysteroids are localized primarily (but not exclusively) in the medulla terminalis (MT) and medulla interna (MI) portions of the eyestalk ganglia. Relative levels of ecdysteroids extracted from the MT and MI fluctuate during the molt cycle. Ecdysone was the predominant ecdysteroid present in the eyestalks. Histological examination of eyestalks revealed two areas of cell bodies in the MT and medulla externa (ME) that release colloidlike substances into the intraganglionic cortical glial spaces. The location of the MT cell bodies corresponds to the pars distalis-X-organ of other crustaceans, but no organ of Bellonci (which has been proposed as a source of ecdysteroidlike compounds in shrimp) was found.
'39). The proecdysial (PE) period is the time of active preparation for shedding of the old exoskeleton. In Uca, the end of anecdysis and the beginning of PE Address reprint requests to Dr.