the lobster was defined as the angle between the path of the lobster from the shelter to its position 30 cm upstream, and a direct path from the shelter to the source. Sham treated animals emerged from the shelter significantly less often when the stimulus was injected into the background flow than in the absence of a stimulus [x2(1,71) = 13.14; P < O.Ol]. Lesioned animals left the shelter significantly less frequently in the presence of the stimulus [x2( 155) = 29.94; P < O.Ol]. Ablates showed no significant differences. In trials where the animals left the shelter, shams were initially “source directed” (~30”) significantly more often than in the premanipulation trials [x*(1,20) = 7.32; P < 0.05]. Lesioned animals did not differ significantly from shams in the number of sourcedirected responses during trials where stimulus was present. Ablates, however, exhibited significantly fewer source-directed responses than shams in this condition [x2(1,26) = 5.45, P < 0.021 (Fig. 1). Our results demonstrate that the loss of an entire antennule interferes with the ability of American lobsters to orient to a far field odor source. We did not find a significant difference in the behavior of animals deprived of only chemoreceptors on one lateral antennule. This may suggest that a sense of flow on both antennules and chemoreception on one is sufficient for normal chemo-orientation. However, in view of the significant depression of overall orientation responses in the lesion treatment group (with stimulus), it may be premature to draw this conclusion from a negative result without further experimentation. This study points to the central role of the lateral antennules and bilateral information processing in,fur,fieZd chemo-orientation in the American lobster. Devine and Atema (3) found that in the near field (<60 cm) odor environment, unilaterally ablated American lobsters make a significantly greater number of incorrect initial turns when presented with a choice between a flavored or unflavored stimulus jet. Our results demonstrate that both the antennules are necessary for a lobster to orient normally when it is sampling in the far more temporally and spatially variable far field odor stimulus environment (1,4,6,7). We thank Christina Manbeck, Dr. David MacMillan, and Dr. Rainer Voigt for their advice and technical assistance in the execution of this project. This work was supported by an REU supplement to NSF grant IBN-9222774 to JA.