52 U. S. BUREAU OF FISHERIES 
areas against the attacks of natural enemies and pollution have con- 
tinued to be the principal fields of shellfish investigation conducted 
by the Bureau in Massachusetts, Connecticut, Virginia, North Caro- 
lina, South Carolina, and Florida. 
To determine the practicability of various methods of oyster cul- 
ture suggested by laboratory experiments, steps have been taken to 
establish experimental oyster beds in localities set aside for this pur- 
pose by State authorities. In cooperation with the South Carolina 
Board of Fisheries and the Works Progress Administration an ex- 
perimental project of this nature was undertaken in South Carolina. 
Experiments on the control of starfish were conducted in Long Island 
Sound and studies of the parasites of the oyster were continued in 
Beaufort, N. C. The work on pulp-mill pollution in York River 
was continued with the cooperation of the Virginia Department of 
Fisheries with the view of determining the chemical nature of the 
substance present in the effluent which was shown by previous investi- 
gation to be harmful to oysters. 
PHYSIOLOGY OF THE OYSTER 
Propagation.—Since successful propagation depends upon the pres- 
ence on oyster beds of a large number of specimens of both sexes 
capable of spawning, the sex changes in the adult oyster present a 
problem of practical importance to the oyster farmer. Study of this 
problem was continued by Dr. Galtsoff and staff at the Woods Hole 
(Mass.) laboratory and at Milford, Conn., where experimental mol- 
lusks individually marked are kept in the outdoor tanks. During 
the first year (1937) 8.0 percent of the males changed to females and 
13.1 percent of the females changed to males, total change in either 
direction being 9.7 percent. In the second year (1938) 11.2 percent. 
of the males changed to females and 12.1 percent of the females be- 
came males, total | percentage of changes in either direction being 
11.5. Sex reversal among oysters that have already changed their 
sex occurs much more often. Out of the total of 32 oysters which 
changed their sex at any time between 1936 and 1938, 22 (69 percent) 
reversed their sex. The results suggest the presence in the popula- 
tion of a group of animals with unstable gonads. 
Development of spawning reactions, which are different in the 
two sexes and are characterized in females by the rhythmicity of 
muscular contractions and discharge of eggs through the gills, fails 
sometimes to keep pace with gonadal changes and results in physi- 
ological intersexuality. Some of the sex-reversed males, possessing 
ripe ovaries, reacted in typically male fashion by discharging egos 
through the cloaca. A complete female spawning reaction “occurred, 
however, at the end of the reproductive season, at which time the 
intersexuality had disappeared. 
Survival and aging of eggs and sperm.—Experiments on fertiliz- 
ability of eggs and their survival in water after being discharged 
by the oyster. were carried out at Woods Hole by Dr. ‘Galtsoff. It 
has been found that more than 50 percent of the eggs will cleave if 
sperm is added after 12 hours, but a very small percentage cleave 
normally if 24 hours elapse between their dischar ge and insemination. 
The life of sperm depends to a certain extent upon its concentration 
in sea water. In sufficient concentration (0.2 g. in 50 ml. of sea 
