Unique asymmetric protrusion of nerve cord in the amphioxus, Branchiostomabelcheri

The amphioxus is the only surviving prevertebrate segmented chordate. In th is animal Hatschek's pit has long been regarded as a putative homologue of the adenohypophysis because of the presence of secretory granules and immun oreactive cells to vertebrate gonadotrophic hormone in this organ. We found that the nerve cord extends a protrusion to the pit along the right side o f the notochord. Furthermore, secretory granules were found not only in the pit but also in the protrusion of the nerve cord. These results suggest th at Hatschek's pit and the nerve protrusion are homologous to the adenohypop hysis and neurohypophysis, respectively. We believe that this is an evidenc e for the presence of the neuroendocrine link between the central nervous s ystem and Hatschek's pit in the amphioxus.