An autoradiographic study of the subcellular water was changed every other day in order to mainlocalization of 2 4 1~m in the branchial hearts of the cephalotain the radiotracer concentration relatively constant. redistribution of the radionuclide between the diffe-The branchial hearts of the molluscan cephalopodOctopus vulgaris can concentrate certain transuranium elements ( 2 4 1~m , 239+240P U) and natural nuclides ( 2 3 2~h , 210Po, 210Pb) very effectively (Guary et al., 1981). In particular, these very small organs, which possess circulatory and excretory functions (Cuenot, 1899;Turchini, 1923;Martin and Harrison, 1966), concentrate the 2 4 1~m present in sea water from atmospheric fallout to a level of about 40 mBq kg-' (1 pCi kg-') wet weight; the concentration factors of 2 4 1~m with respect to sea water in the branchial hearts, as well as those of 2 3 9 f 2 4 0~~, 232Th, 2 ' 0~o and 210Pb, are as high as 104 (Guary et al., 1981). Moreover, it has been demonstrated that these organs are able to accumulate vanadium (Miramand and Guary, 1980) and cobalt (Nakahara et al., 1979) with concentration factors of 3 X 103 and 2 X 104, respectively. These data suggest that the branchial hearts of the octopus have considerable potential as monitors of transuranics, and probably certain other elements, in the marine environment. It is accordingly important that the physiology of the branchial hearts be understood and that the intracellular sites of binding of radionuclides in these organs be established.An Octopus vulgaris female (360 g) was caught in the littoral zone off Monaco and placed in filtered and aerated sea water at 13' & 1 Co. The sea water (4 1) had been spiked previously with 241Am (assumed to be in +3 state) at a concentration of 1 kBq 1-' (30 nCi I-').Throughout the 10-d exposure period, the spiked sea rent organs. During these two phases the cephalopod was monitored regularly by gamma-spectrometry using a 3" NaI (Tl) crystal. After the 70-d period, the cephalopod (by now weighing 680 g) was dissected. Branchial hearts were removed immediately from the living cephalopod, and several small pieces were fixed in Bouin's solution and gamma-counted at the same time as the other tissues and organs. It was particularly noteworthy that branchial hearts, which account for only 0.2 % of the body weight, contained 99 % of the total radioactive body burden. Further details concerning the uptake, loss and distribution of the radionuclide have been published (Guary, 1980)., The concentration of activity in the branchial hearts was about 4 kBq g-' (0.1 pCi g-l). After 24 h fixation, the branchial hearts were dehydrated and embedded in paraffin and sectioned at 5 pm. Sections were collected on glass slides, dried and dewaxed. Autoradiographs were prepared with Ilford K 2 nuclear emulsion (diluted with 1 % glycerin solution at 43" C) by the dipping technique (Rogers, 1973). Emulsion-coated slides were dehydrated and exposed for 15 d in light-proof boxes at 4 "C. Exposed autoradiographs were developed, fixed...
