546 U. S. BUREAU OF FISHERIES 
the amount did not exceed 5 milligrams per liter, especially in the 
upper water. In some lakes there was a marked increase of silica in 
the lower water; in Trout Lake the surface water contained 3 milli- 
grams and the bottom water (30 meters) 8 milligrams per liter on 
July 9, 1926. 
The chlorides varied from 0.53 to 3.1 milligrams per liter of water; 
in most instances the amount was between 1 and 2 milligrams per 
liter. 
Two to 10 liter samples of centrifuged water were evaporated for 
the purpose of obtaining the residue. ‘These residues varied in 
amount from 12 milligrams to 88 milligrams per liter of water in the 
upper stratum. A maximum of 144 milligrams per liter was obtained 
in the lower water of one lake. In this connection it may be noted 
that the hard-water lakes of southeastern Wisconsin yield from 165 
to 255 milligrams of residue per liter. These residues are now being 
used for the determination of the quantity of organic carbon, and 
quantitative determinations of other substances therein are also con- 
templated. 
A Foerst electric centrifuge was used for the purpose of making a 
quantitative study of the plankton. This material was dried in an 
oven, weighed, ashed in an electric furnace, and then weighed a 
second time in order to ascertain how much organic matter it con- 
tained. The quantity of this organic matter varied from a minimum 
of 265 milligrams per cubic meter of water to a maximum of 10,875 
milligrams. In most of the lakes, however, the amount ranged from 
800 to 2,000 milligrams per cubic meter. 
SHELLFISH AND TERRAPIN 
OYSTERS 
Owing to the increased appropriations for the oyster investiga- 
tions, the program of work relating to this important fishery was 
considerably extended under the supervision of Dr. P. S. Galtsoff. 
The investigations made during the fiscal year consisted in (1) sur- 
veying the natural oyster beds and reefs, (2) study of the spawning 
of the oyster, (8) studies of the behavior of the oyster larve and of 
the conditions controlling setting in northern waters, (4) experi- 
ments in oyster-seed production and collection, and (5) study of the 
oyster drill. 
SURVEYS OF THE NATURAL OYSTER REEFS AND BEDS 
Texas—In compliance with the request of the game, fish, and 
oyster commissioner of Texas, a survey of coastal waters was made by 
Dr. P. S. Galtsoff during February and March, 1926. The purpose 
of the survey was to determine what practical measures should be 
adopted in order to prevent further depletion of the natural reefs 
and to maintain, or if possible to increase, the production of oysters 
in the State. 
The survey covered the region extending 170 miles along the coast 
of the Gulf of Mexico, from Corpus Christi to Galveston. Field 
observations were made in cooperation with the State authorities, 
who assigned the State boat Pearl to the investigator for this pur- 
