Theory tetrapods

Snakes are used here in a paradigmatic sense, not in an actual sense, applied to fossil and extant snakes. The example is also used only in order to illustrate the immunization of the logically subordinated hierarchy per se. As far as the classification (or relationships) of snakes are concerned, the old theory (snakes are not tetrapods and have no legs) has been replaced by a new theory (snakes are tetrapods with modified legs), for which an independent test can be postulated, but see below for the nature of test of specific hypotheses of relationships based on the application of parsimony. 

The chemical shifts allowed the local order parameters to be computed which indicated the uniaxial to biaxial nematic phase transition. The nematic phase of a deuterated fiuorenone nematogen has been studied by NMR and X-ray and evidence for biaxial order close to its glass transition temperature has been inferred. The possible symmetries of the biaxial nematic phase have been examined based on experimental results and it is concluded that a monoclinic symmetry rather than an orthorhombic symmetry that is more likely to be the cause for the observed phase biaxiality in thermotropic bent-core and calamitic-tetrapode nematic systems. Density functional theory has been employed in a detailed conformational study of a bent-core mesogen The chemical shielding... 

Past theories have identified the limits of ectoderm in the mouth as central to the determination of where teeth develop (Jollie 1968 cf. Smith and Coates 1998, fig. 8). However, this view takes no account of the widespread occurrence of denticulated plates deep within the pharynx of non-tetrapod vertebrates. These include a major, successful, group of teleosts which feed entirely as pharyngognaths, and have teeth only on the last gill arch. The model animal for developmental research in fish, the zebrafish, is one of these, and we predict that experimental data will show that this is an endodermally derived pattern. Moreover, one direction for future comparative research in all appropriate model taxa could be towards the identification of those genes which are expressed in, and give pattern and positional information to, the endoderm in relation to initiation of the dentition. Already, we know that endoderm is essential for tooth formation in amphibians, and snspect that it may be so for other gnathostomes. Finally, it shonld be possible to examine where the boundary forms between ectoderm and endoderm, and the role of this bonndary in setting up positional information for the dentition. 

---