ULTRASTRUCTURAL ASPECTS OF THE LATERAL-LINE ORGANS OF THE NORMAL AND HYPOPHYSECTOMIZED CLAWED TOAD, XENOPUS LAEVIS (DAUDIN)

SUMMARY The fine structure of the lateral-line organ was inspected in eight adult specimens of the clawed toad, Xenopus laevis (Daudin), 21 days after hypophysectomy and in eight intact controls. In both groups the occurrence of cells termed «light», «intermediate» and «dark» cells according to the electron-density of their jaloplasm, was observed. Likewise, differences were noticed in the nuclear and mitochondrial characteristics of these cells, and in both the amount and distribution of their synaptic vesicles and synaptic bodies. We suggest that these cells represent progressive changes of the same receptor type, rather than three different cell types. The purpose of the present study was to examine the ultrastructural changes, if any, of the neuromasts correlated to the impairment of their chemosensitivity resulting from hypophysectomy. These findings are discussed in relation to the duration of the experimental treatment and to the functional significance of the sensory cells.