1. U. Stenkewitz (), Faculty of Life and Environmental Sciences, Univ. of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland.
2. US and Ó. K. Nielsen, Icelandic Inst. of Natural History, Garðabær, Iceland.
3. US and K. Skírnisson, Inst. for Experimental Pathology, Univ. of Iceland, Keldur, Reykjavík, Iceland.
4. G. Stefánsson, Science Inst., Univ. of Iceland, Reykjavik, Iceland