PROGRESS IN BIOLOGICAL INQUIRIES, 1939 65 
the Connecticut seed-oyster producing section. The methods em- 
ployed in this study were the same as those used during the 2 previous 
years. 
The development of gonads was followed since May 18, 1939, by 
making weekly inspection trips over the entire area under observa- 
tion. ‘By June 23, the average thickness of the gonad layer of oysters 
was about 2.8 mm., somewhat less than during the corresponding 
period of 1938 (3.8 mm.) and consideraly below that of 1937 (4.3 
mm.). From June 23 to June 28 the gonads increased to 3.1 mm. 
By this time many of the oysters were completely ripe, and some of 
them already had partial! y discharged their spawn. Two days 
later, partially spawned animais were found at almost all stations, 
and the average thickness of gonad layer decreased to 2.7 mm. 
eee from comparatively shallow areas were the first to spawn. 
Spawning soon began to be of more general occurrence, and on June 
30 some oysters with partially discharged gonads were found at 
almost all depths ranging from mean low-water mark to 40 feet. 
As in the previous year, the temperature of water prior to and 
during the early period of spawning was several degrees below 
20.0° C. 
Systematic observations on the setting of oysters were made at 10 
stations at Stratford Point, and 6 stations at Welchs Point. Addi- 
tional weekly observations were made at 15 other stations located in 
different sections of the Connecticut oyster-growing area. The first 
light set of the year was recorded at Stratford Point on and around 
July 17, 1989, about 2 weeks after the first general spawning, at depths 
ranging from mean low water to 50 feet. Between July 20 and 24 
the ‘intensity of setting increased considerably, but decreased sharply 
after July 31. There was no setting between ‘August 3and 17. From 
then on until September 21, scattered and very ‘light sets took place 
at medium depths and in shallow areas. Observations were continued 
until the first part of October but no new spat were found after 
September 21. 
In the Welchs Point area the first. setting occurred between July 18 
end 21, and the last set was recorded on September 12. The peak of 
setting took place between July 25 and August 1. During that period 
setting was exceedingly heavy, especially at 30-foot depth, sometimes 
averaging over 380 spat per shell. In some samples, shells contaming 
as many as 1,000 spat were found. After August 1 the intensity of 
setting sharply declined for the rest of the season. 
Setting of oysters in 1939 was probably the heaviest since 1930, and 
certainly much heavier than in 1937 and 1938, although the quantity 
of spawn developed in 1939 was very small. This observation dis- 
proves the old idea that a good setting can be expected only in those 
years when the gonads develop large quantities of spawn. Of special 
interest is the observation that in 1939 the spawning and heavy set- 
ting of oysters took place during a period of prolonged and very 
severe drought. Prior to and during that period the river discharge, 
as well as the amount of precipitation, was exceedingly low. Con- 
sidering the fact that setting in 1939 was much heavier than in many 
previous years, the question naturally arises whether the inflow of 
fresh water carrying certain substances is really important in 
inducing the setting of larvae. 
