~16- time is one-eighth thet of the pretest level; is an increase in activity. subsequently there Since both the total activity and the long-lived activity increased by approximately equivalent amounts, the increase must be due to an increased net rate of uptake, reflecting a change in the physiology of the crab or 4 change in the conditions in the environment, availability of, leading to a greater in this case, Csl37 to the crab. The latter possibility is the more eastly explained by the observations. The same pattern of decrease in activity followed by a rise is evident in the gut and liver of the crab, the leaves of the shruts, Scaevole and Messerschmidia, and the muscle of the field rat, Rattus exulans, from Janet (Engebi) Island, which is also in the northern part of Eniwetok Atoll.+9 During the first 200 days (May - November, 1954) rainfall at Eniwetok averaged about 4 incnes per month while for the following 150 days (December - April) the average monthly rainfall was about 0.3 inches (Fig.7). Since individual variation in the level of activity is great there would be little reason to accept the validity of the correlation were it not repeated in the plants and in rat muscle, which are also high in Csli37 content, (56% of the total activity in the latter). It appears likely, therefore, that the changes in activity in the crab and rat muscle reflect some underlying mechanism associated with rainfall which is responsible for changes in the levels of activity itn the plants. There could be one or several factors involved in the association with rainfall including, for example, such things gor as