PROGRESS IN BIOLOGICAL INQUIRIES, 1937 43 



and planting sliells. Studies in, the life history and distribution of the 

 starfish disclose the inadequacy of present methods of control and 

 demonstrate that in Long Island Sound control is an interstate prob- 

 lem. Experiments with the use of chemicals in the eradication of 

 starfish are very promising and indicate that chemical control may 

 soon be put on a practical basis. The work on pulp mill pollution 

 provides convincing evidence of the toxicity of pulp mill etliuent with 

 the result that practical steps are being undertaken by interested 

 parties to abate this hazard. 



PHYSIOLOGY OF THE OYSTER 



Physiological investigations on the oyster were carried out by Dr. 

 Galtsolf and staff at the Woods Hole, Mass., laboratory. Studies were 

 ■continued on sex changes in adult oysters, accunuUation and storage 

 of iron in oyster tissues, and the effect of industrial pollution on 

 respiration. 



Sex changes. — The work on sex change Avas undertaken with the 

 view of obtaining additional evidence of sex reversal in adult oysters. 

 Methods used by previous investigators are open to criticism. The 

 method of comparing sex ratios of oyster populations is obviouslj' 

 inade(;[uate where both types of change — from male to female and 

 from female to male — are involved. The method of examining the 

 gonads of living mollusks through holes bored in the shell is ob- 

 jectionable because of the unknown effect of injury on the presumably 

 unstable gonad of the mollusk. 



The method used in this investigation consisted in determining 

 the sex of the oyster by inducing ovulation or ejaculation by in- 

 creased temperature and chemical stimulation (Galtsoff, 1930, Proc. 

 Nat. Acad. Sci., 16, No. 9, pp. 555-559). Of each of the 202 adult 

 oysters tested at Woods Hole during the summer of 1936 an indi- 

 vidual record of the spawning reaction was obtained and the dis- 

 charged products were examined under a microscope. Each oyster 

 was then measured and marked by engraving a number on its right 

 shell. Elaborate precautions were taken to avoid any possibility of 

 mismarking. Oysters were then transferred to Milford, Conn., where 

 they were kept in large tidal tanks. 



During the summer of 1937, the sex of these marked oysters was 

 redetermined by the same method used in 1936. It was found that 

 ■9.7 percent of the oysters had reversed their sex. The percentage of 

 reversals was consiclerably higher among females (13.1 percent) than 

 among males (8.0 percent). The mortality during the year was only 

 7.04 percent, probably a normal death rate among adult oysters. 



As previous observations by Dr. Galtsoff have shown, ovulation of 

 the female is accompanied by typical rhythmical contractions of the 

 adductor muscle and passage of eggs through the gills, while in the 

 male ejaculation proceeds through the cloaca and does not involve 

 specific behavior of the adductor. In the sex reversed males the 

 physiological set-up of the organism changes with the change of 

 sex and a ty])ical female reaction develops. In several instances, 

 however, the' development of this reaction lagged, the newly formed 

 female still acting as a male by discharging eggs through the cloaca 

 and failing to develop rhythmical contractions of the adductor. Its 

 kymograph record could easily have been mistaken for a male re- 



