SOME EGG-LAYING HABITS OF AMPHITRITE ORNATA VERRILL

Abstract

1. In Amphritite ornata Verrill, the egg-laying reflex is closely associated with the time of spring tide ; the height of any given period of egg-laying always occurs within two days of the time of new or full moon. Periods of oviposition occur in June, July and August. 2. The moon does not have any direct influence in producing the period of sexual activity. It is probable that the tide also has little, if any, direct effect on the process. 3. At spring tide, the worms feed more actively, the food supply is more abundant and the sand flats have a higher temperature. As this period approaches we also find a more rapid growth and development of immature eggs and sperm. Therefore, the period of sexual activity is closely associated with a synchronous period of greater bodily activity, and this greater vigor of the animal is induced by conditions that depend upon the tide. In this way we may explain how oviposition in Amphritite has become a sort of reflex habit associated with the time of spring tide. 4. When a worm is sexually mature, the cœlomic fluid contains cœlomic corpuscles and eggs in various stages of development. At oviposition the worm extrudes ripe eggs, and toward the end of the process some of the immature ones, but always retains the much smaller cœlomic corpuscles. 5. Since the mature eggs sink faster in sea-water than the smaller immature ones, and all eggs sink faster than the cœlomic corpuscles, it is believed that the larger eggs have a greater density than the other bodies in the cœlomic fluid ; and it is entirely probable that the apparent selection of ripe eggs and the rejection of immature ones is due to the different effects produced by nephridial currents upon bodies of apparently different densities. 6. The position of the nephridial sacs, and the arrangement of cilia on the nephrostomes and within the sacs, is such that we may regard the nephridia as a set of settling basins in which the separation takes place. Contractions of the worm's body then aid in expelling the ripe eggs from the nephridial sacs.