204 
bulletin of the bureau op fisheries. 
That these variations in weight have no special significance is indicated by com- 
parison with the variations in the weights of oysters kept in the aquarium during the 
summer but not exposed to tar. 
Initial 
weight. 
Weight after 
five weeks. 
Grams. 
66. 5 
76. 0 
244-0 
147.0 
Grams. 
66. 0 
76. 5 
243. 0 
151. 0 
When opened all were found to be normal in appearance and function. No odor 
of tar was detectable in the shell contents of the oysters, although an abundance of tar 
was left in the jars at the end of the experiment. Smears of tar were also still present 
on the outside of the oyster shells. 
These experiments indicate that even intimate contact with water-gas tar does not 
injure oysters in the course of nine weeks, provided facilities for defense in the form of 
moving water frequently renewed are available. 
SERIES III. 
Experiment i . — A small oyster was first pried open and injected with 0.5 c. c. of water- 
gas tar. It was then put in a jar of running sea water. It remained tightly closed 
during the next two hours. On the next day it was found to be quite normal. It was 
open and apparently feeding, but closed when stimulated. Drops of tar near it indicated 
that the foreign material had been ejected. One week later it still appeared entirely 
normal. It was then again injected with 0.5 c. c. of tar, and was now put in stagnant 
sea water. Four days later it did not, when stimulated, close as readily and tightly as a 
normal oyster. It was then opened and foimd normal in its heartbeat and in con- 
tractility of the bivalve muscle, but the mantle was not normally responsive to mechanical 
stimulus. 
This experiment indicates that when an oyster ingests tar and can not get rid of it 
because the surrounding water is stagnant, some impairment of the sensory apparatus 
in the mantle results. This interferes with certain activities of the oyster, prevents 
normal closure, and eventually causes degeneration of muscular and other tissues. 
Experiment 2 . — Three medium-sized oysters were each injected with about 1.5 c. c. 
of water-gas tar and then put in separate jars of running sea water. Some time after 
they were seen in each case to open slightly and in a few minutes close violently so as to 
eject masses of tar. This process was repeated a number of times in the course of one 
to three hours after injection. They then remained constantly closed for some time, but 
were foimd normally open on the following day. They were left in the running sea 
v/ater for a period of eight weeks and behaved throughout that time like control oysters 
in the aquarium. As it was then necessary to terminate the experiments, the oysters were 
