64 U. S. BUREAU OF FISHERIES 
lished in the Biological Bulletin, Vols. 74, 75, and 78. It has been 
demonstrated by this investigation that an old concept of a single 
critical temperature that induces spawning in oy sters is no longer 
tenable. Depending on the physiological state of ripeness, the oy ster 
may spawn at various temperatures between 63° and 95° Milh A 
thermic stimulus alone often is not sufficient to induce spawning, 
and a combined action of temperature and chemical stimulation are 
necessary to produce the desired effect. However, a number of 
chemical compounds were found to be effective in inducing spawning 
of the male oyster. 
These physiological studies provide a key to a practical method 
of controlling the spawning of oysters under natural conditions. To 
speed up the discharge of cele ripe oysters from deep bottoms 
should be brought into shallow, warm water of the inshore areas and 
left there for a few days. Aditiestal stimulus can be provided by 
opening a few ripe oysters, mincing their meats in sea water, and 
scattering this mixture over the bed of spawners. The method y 
tried with success by some of the oyster growers of Long basal 
Sound and in British Columbia. 
Since it has been demonstrated that the proximity of both sexes 
is essential for a successful spawning of oysters, it would be ex- 
pected that a considerable disparity in the sex ratio may interfere 
with their propagation. Previous field observations have demon- 
strated the prevalence of females among the adult oysters on certain 
oyster bottoms. An investigation of the problem, initiated by Dr. 
Galtsoff in 1937 and continued through the present year, showed 
that the increase in the female population is primarily due to the 
sex change among adult oysters. Continuing this study during the 
present fiscal year, 290 individually marked oysters, which were kept 
at Woods Hole and Milford, were retested for spawning. An analy- 
sis of the records obtamed during the 3 consecutive summers shows 
that sex change among adult oysters occurs in both directions; 1. e., 
from male to female as well as from female to male. It is interesting 
to note, however, that during the 3-year period 17.6 percent of the 
oysters under observation changed from female to male, as compared 
with 31.2 percent changes from male to female. Thus it is obvious 
that in spite of the change of a certain number of females to males, 
the proportion of females in the oyster population steadily increases 
with age. 
From these data it is apparent that the maintenance of a more or 
less normal sex ratio is essential for successful propagation of oysters. 
For practical purposes, the problem can be solved by adding each 
year a sufficient number of 3-year-old oysters to the stock of old 
spawners. 
A study of sex reversal in adult oysters is being continued with 
the view of determining genetic and environmental factors which 
control these changes. 
Long Island Sound.—Observations on the development of gonads, 
spawning, setting, and mortality of oysters were continued ‘by iDie 
Victor L. Loosanoff and James B. Engle, of the Bureau of Fisheries 
Laboratory, Milford, Conn. The area under investigation, extending 
for about 30 miles from Bridgeport Harbor to Morgan Point, east 
of New Haven, represents the largest and most important part of 
