in the catches was made to determine if the difference in counts between net hauls and between stations could be accounted for by the type of organism in the catch. Although the catches varied considerably both quantitatively and qualitatively, there was strong evidence that activity of the samples was not associated with the presence of any one group of organisms. Autoradiographs of a dried plankton sample showed that the activity was usually associated with inanimate objects, but even when the organisms were active the association was not with any one particuler group (see Section 4.9.1). evidence was obtained from the paired hauls, Further in which the activity of the samples often varied but the composition of the catch was similar. For example, the catch in net B and net D at Bogallua appeared similar in composition - foraminiférans: principally, and some snails, copepods and a few miscellaneous eggs and arrow worms - but the sample from net B was 7 times more active than the sample from net D (1,160,000 d/m/g + 155,000 d/m/g). Since net B was of finer mesh than D (173 and 74 meshes per inch respectively) it might be thought that some smsll radioactive organism was escaping the D net and was being caught in B, but microscopic examination of the eatches did not demonstrate this to be true. 1s believed that the fine-meshed net was more efficient in capturing suspended, inanimate radioactive particles. Results. The radioactivity in plankton samples is recorded in Table 2. ~ 23 - It