66 
BULLETIN OF THE BUREAU OF FISHERIES 
attains 20° C. While in Galveston Bay the temperature was sufficiently high during 
part of the time early in March, no spawning took place because the germ cells in the 
gonads had not reached maturity. No well-formed eggs or active sperms were found 
in the oysters before March 18. Because of the very rapid spring rise in water tem- 
MAY JUNE 
29 
2 4 6 8 10 12 14 16 IB 20 22 24 26 28 30 I 3 3 7 9 II 13 13 17 19 21 23 25 27 29 
JULY AUGUST 
Figure 9.— Charts showing daily temperature of water in Oflatts Bayou, Galveston, from March to August, 
1929. Daily temperature was calculated as the average of the 24 hourly thermograph readings. The 
thermograph bulb was about 2J4 feet below low tide level at the edge of a 30-foot channel 
perature the critical temperature for spawning was reached in advance of maturation 
of the gonads. 
The maximum of the spawning period occurred in May and June, during which 
time the water temperature was usually well above 25° C. and had been so since the 
end of Ad arch. This is strikingly in contrast to the observations of Prytherch 
