Ph. D. (Degree) Title: VARIATIONS IN SALINITY TOLERANCE IN THE PACIFIC

Eggs, larvae and adults of the four subspecies of Hy la regilla occurring in Oregon as given by Jameson, Mackey and Richmond (1966) were collected and subjected to salt stress in a series of graded seawaters. It was found that in all cases adults were more tolerant than larvae and larvae were more tolerant than eggs. It was also found that animals in all stages taken from the area extending westward from the crest of the Oregon Coast Range to the sea, designated as the range of Hy la regilla pacifica, were more tolerant of elevated salt levels in their ambient medium than animals from the three other subspecies areas in Oregon. Observations were made of the effect of elevated salinities on the eggs and the development of the embryos with respect to the vitelline membranes, the closure of the blastopore and neurulation. Mechanisms were postulated to explain the observed differences in tolerance to salt stress