spectra at higher temperatures; in fact, for several H4WL4 tungsten complexes, where L is a phosphine or arsine ligand, the nonrigidity limit is reached above room temperature.7 (7) (a) B.

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Abstract.-The chemical taxonomic relationship of microorganisms has been studied through the hydrocarbon fraction of their chemical constituents. The diagenesis and biological transformations of some hydrocarbons in sediments is suggested, as a result of this information.Various compounds of presumed biological origin have been isolated from petroleum,' ancient sediments,2-4 and meteorites.5 Among these classes of organic compounds, the hydrocarbons have probably received the most attention. Meinscheinr found that the extracts of soil contained more odd than even carbon-numbered normal paraffins. Bray' reported that the ratio of odd over even carbon-numbered n-paraffins is significant in Recent sediments, approximately 2.4 to 5.5. However, the value decreases for older sediments, and it is close to 1.0 in petroleum. The isoprenoid hydrocarbons with the regular headtail-head-tail linkage have been taken to be the residue of life forms.3Barghoorn and his co-workers8' 9 claimed to have found blue-green algae and bacterialike microfossils in Precambrian rocks. It is very important to obtain confirmatory evidence for the existence of these primitive microorganisms in the Precambrian period.Chemical criteria can be used as confirmatory evidence for classifying living organisms which were previously identified solely on the basis of morphologic characteristics. Chemistry may have more to contribute than any morphological analysis, not only because of the relative evanescence of most plant tissues in geological deposits, but also because the biochemistry of evolutionary processes may be deduced from the presence of compounds from known diagenic pathways.The evolutionary step from the procaryotic cell (blue-green algae and bacteria) to the eucaryotic cell (green algae, fungi, protozoa, higher plants, and animals) is recognized by the appearance (or presence, in some cases) of nuclear membrane, mitotic division, chromosome number, cytoplasmic streaming, and mitochondria in the eucaryotic cell. Since lipids are important constituents of cytoplasmic and intracellular membranes, chemical taxonomic studies have been made to determine whether such evolutionary transitions are reflected at the molecular level.

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