114 S. M. Marshall and A. P. Orr 



well, but the maximum volume filtered was just over 2 mi in 24 hours (Table I). The 

 digestion (68-76%), was decidedly lower than that found using Syracosphaera 

 labelled with ^'^p^ in which it was usually over 90%. This may be due to the presence 

 on its surface of a layer of coccoliths which would contain "C in the form of calcium 

 carbonate. 



The rate of production of faecal pellets was not high in any of the experiments with 

 ^*C, the most rapid being found in a Calanus in Skeletonema culture, which produced 

 an average of one every twelve minutes. It has been found that even with a much 

 more rapid production, digestion of the phosphorus-containing fraction remains 

 high. 



ACKNOWLEDGEMENTS 



The experiments with ^*C labelled cultures were carried out at The Laboratory, 

 Plymouth, and we are very grateful to the Director and staff for their help. More 

 especially we wish to thank Dr. H. W. Harvey and Dr. B. C. Abbott for their advice 

 and assistance, and Dr. M. W. Parke and Miss D. Ballantine for supplying us with 

 cultures. 



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