NEURONS IN THE 3RD ABDOMINAL-GANGLION OF THE EARLY POSTNATAL CRAYFISH- A QUANTITATIVE AND ULTRASTRUCTURAL-STUDY

Ultrastructural data on the third abdominal ganglion of the crayfish w as heretofore only available for adult individuals. The fine structure of neurons in the adult that are involved in the escape response has been described in detail, but no similar data existed for the postnata l individual. An increase in the number of neurons in the third abdomi nal ganglion during postnatal stages had been reported, which suggeste d that several changes in the features of neurons may occur. Here we d escribe the general anatomy and ultrastructure of the early postnatal third abdominal ganglion, with emphasis on neurons, and we compare the ir characteristics to those of the adult. Abdominal ganglia of 56 cray fish of 0, 8, 10, 18, 25, 50, 110, and 150 postnatal days were process ed under cacodylate buffered aldehyde fixatives, osmicated, embedded i n plastic, sectioned, and examined by light and electron microscopy. T he anatomy of postnatal ganglia is homologous to the anatomy of the ad ult ganglia except that the perineurium is not developed in postnatals . The area of neurons within the postnatal ganglion shows no stratific ation, but neurons are grouped in nuclei according to their size. Neur ons constitute a homogeneous population in different stages of maturit y, as revealed particularly by the ultrastructure of the nucleolus. Po stnatal development is evident in the perineurium, which may provide s tructural support to the ganglion.