584 Annals New York Academy of Sciences 



microbiology and micropaleontology provides numerous examples of the 

 successful use of fine morphological characteristics (involving features less 

 than 1 /x in size) in the identification of protobionta. 



The blue-green algal genus Oscillatoria has 160 morphologically distinct 

 taxa, 28 of which are less than 1 ^t in diameter but they are still amenable to 

 morphological characterization (Hollerbach et al., 1953). As early as 1871, 

 optical microscopy was sufficiently advanced to allow Pfitzer to establish two 

 new genera Neidiuni and Anomoeoneis, that were formerly included in Navicnla, 

 by observing morphological features less than 0.3 ju in size. The recent work 

 of Hay flick (1962) established that primary, atypical pneumonia in humans 

 is caused by a pleura pnetimouia-Uke organism (PPLO), less than 0.3 n in size. 

 The same detailed morphological observation is also used in characterization of 

 microfossils. Recently, Evitt (19616 and 1962) has shown that the group 

 of Hyslrichospheres (Precambrain to Recent) consists of polyphyletic members. 

 This finding was again based upon the observation of fine morphology, which 

 involved the examination of the number of processes, spines, and the plate 

 structures. Most biologists agree that the microscopical examination of fine 

 morphological features (1 /z or less in size) is not only possible but it is a common 

 practice in systematic zoology and botany. 



Modern biological microscopes, if properly used by experienced investi- 

 gators, can resolve objects as small as 0.2 /x in diameter. The theoretical 

 limit of resolution is 0.10 ^t. Clearly, it is quite possible to observe morpho- 

 logical features in the 0.3 to 0.5 n range. Fitch and Anders argued that one 

 of the organized elements embedded in mineral matter in one of the thin sec- 

 tions of Nagy et al. (1962) cannot be characterized because the spines are 

 approximately 0.3 ji long and the resolution of a microscope which they be- 

 lieved to be equipped with a regular, high dry objective is 0.3 ju- This argu- 

 ment is in error because the spines on this organized element were observed 

 with a X/O oil immersion objective, with a numerical aperture of 1.15, which 

 gave a lower limit of resolution of 0.22 ^i. The transparency of the embedding 

 mineral (magnesium sulfate), its lack of color in the thin section and the lack of 

 significant differences in refractive indices in this portion of the microscopical 

 preparation prevented any serious interference from attaining the necessary 

 resolution. 



Fitch and Anders (1963) proposed a set of criteria to establish that certain 

 objects are microfossils. Their criteria are essentially the customary defini- 

 tion of life. They suggested that to be able to prove that the organized ele- 

 ments are indigenous and extraterrestrial microfossils one must show (1) that 

 they have characteristic morphologies, (2) show some evidence of propagation, 

 and (3) show signs of metaboHc processes. 



Their first point needs no further discussion. One may reply to their second 

 requirement by noting that adjoining organized elements have been observed 

 embedded in minerals. This raises the possibility of either copulation or 

 division (figurp: 6c). Similar objects (but solitarily) were often found in the 

 mineral matrix (figure db). A less direct indication may be derived from the 

 possible presence of deoxyribonucleic acid- (DNA)-type material, which will 

 be discussed in another chapter. Finally, the presence of what may be bio- 



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