Essence of the Designs of Gas Exchangers — the Imperative Concepts
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Gas exchangers have developed and tractably adapted with the respiratory requirements of whole organisms in different states and habitats. The environmental factors that have profoundly influenced the general phenotype have simultaneously shaped the designs of the gas exchangers. On that account, the functional constructs of the gas exchangers cannot be understood without recognizing both these drives as well as the underlying physical principles that govern organismal biology. Form is a gestalt of structure. The importance of morphology and physiology as investigative approaches towards conceptual understanding of comparative evolution by natural selection cannot be overstated (Cracraft 1983; Duncker 1985; Greenberg 1985; Huey 1987). It should, nonetheless, be cautioned that it is oftentimes possible to mislead these aspects (especially morphology) in accurate reconstruction of phylogeny. For example, the so-called cryptic species (e.g., Bruna et al. 1996) or sibling species (e.g., Mayr 1942) are morphologically identical but genetically different. Such mismatched animals can be utilized to investigate the ecological and evolutionary events and mechanisms which enforce congruent morphologies. Until recently, morphological characteristics were the primary and practically the only means of organizing and classifying animals (e.g., Eldredge 1993; Rieppel 1993). Molecular genetics now offers a powerful means of supplementing morphological observations and validating phylogenetic relationships between different animals (e.g., Sibley and Ahlquish 1990; Graur 1993; Larson and Chippindale 1993; Luckett and Hartenberger 1993; Blair 1994; Hedges and Sibley 1994; Janke et al. 1994; Averof and Akam 1995; Penny and Hasegwa 1997).