However, the same relationship can be found in Table 8 , which is based on the average values of similar species. l. Muscle consistently has the lowest specific activity regardless of species. "Liver" or digestive gland is the only tissue sampled, other than muscle, which is not subject to external contamination. It rarely has a higher specific activity than the digestive tract and is always more radioactive than muscle. The relative specific activity of the gill varies with the species. In the clams the gills, which are the food gathering organ, have the highest activity, exclusive of the digestive tract with its content. In those snails with a gill the “liver” is the more active. The liver is also more active than the gill in the crabs. The digestive tract with its content is usually the most radioactive portion. Its activity is highly vari- able, however, even within a species from the same station. Shell and carapace are also highly variable in specific activity. The following rankings of tissues in descending order of specifie activity with individual exceptions are: a. Clams: (1) digestive tract (visceral mass with contents ) 2 gill 4) mantle 3 5 liver" muscle - 4) -