EXPERIMENTAL STUDIES ON THE ENDOCRINOLOGY AND REPRODUCTIVE BIOLOGY OF THE VIVIPAROUS POLYCHAETE ANNELID, NEREIS LIMNICOLA JOHNSON

¹ Department of Zoology and its Cancer Research Genetics Laboratory, University of California, Berkeley, California

1. The relationship of gametic and somatic maturation in the atokous polychaete, Nereis limnicola, differs significantly from the general nereid pattern. In this viviparous species muscle histolysis and the decrease in the coelomocyte concentration are delayed with respect to the onset of gamete maturation, and occur, instead, in association with the intracoelomic development of the offspring. However, worms with mature gametes are unable to regenerate lost caudal segments.

2. The cerebral ganglion of N. limnicola exerts an inhibitory influence on the maturation of sperm and oöcytes. Brain removal results in the precocious appearance of normal larvae in the coelom. This effect is prevented by implanting a brain into the coelom of the decerebrate worms.

3. Histological examination of brains that had been implanted for three weeks revealed that the infracerebral gland epithelium was present and normal in appearance.

4. Decerebration of worms containing coelomic larvae did not delay or accelerate larval development.

5. The effect of implanting parts of brains on gamete maturation of decerebrate worms was studied, and the results indicated that the dorsal part of the brain, which contains many neurosecretory cells, and the ventral part of the brain, on which is located the infracerebral gland epithelium, had approximately equivalent inhibitory activity when implanted alone or together, but this inhibitory effect on oögenesis was not as great as that produced by an implanted intact brain. These results are interpreted to mean that the infracerebral gland epithelium and neurosecretory cells of the brain may form a neuroendocrine system, the integrity of which is essential for secretion of the maturation-inhibiting hormone at normal levels.