ONTOGENY OF NEUROENDOCRINE CENTERS IN THE EYESTALK OF HOMARUS-GAMMARUS EMBRYOS - AN ANATOMICAL AND HORMONAL APPROACH

The ontogeny of the eyestalk neuroendocrine centers of the European lo bster, Homarus gammarus, throughout embryonic development has been stu died using light and electron microscopy, and the localization of spec ific neuroendocrine substances has been identified by immunocytochemis try. The procephalic lobes, which are the prospective eyestalks, devel op progressively during embryonic development. In the nauplius stage t wo neuron masses are well defined. The visual structure originates fro m one of them and the neuroendocrine structure from the other. The fou r definitive optic ganglia are present at the mid-metanauplius stage a nd retain their appearance and location in larvae and adults. The orga n of Bellonci, an internal sensory structure, appears at the mid-metan auplius stage and is mainly characterized by onion bodies. The medulla terminalis X-organ complex, an important neuroendocrine system, is pr esent and already functional at the beginning of the embryonic metanau plius stage. Two neurohormones have been visualized immunocytochemical ly : the crustacean hyperglycemic hormone (CHH) and the gonad inhibiti ng hormone (GIH). Both neuropeptides are localized in the perikarya of neuroendocrine cells of the X-organ as well as in their tracts joinin g the presumptive sinus gland. However, the sinus gland has only been observed in the early larval stages just after hatching.