Various endogenous and environmental challenges of homoiostasis have resulted in the evolution of apparently quite different mechanisms for the same or similar functions in individual representatives of the animal kingdom. One of the prominent achievements of comparative physiology over the last few decades has been the description of regula- tory features common to many studied species beyond the extreme diversity of their morphological forms. Delineation offunctional princi- ples universally applicable to the physiology and biochemistry of living systems became often possible through technical advances in the devel- opment of numerous new techniques, in many cases modified and adopted from other fields of science, but also by approaching certain problems using multifactorial analysis. The advance in technology has facilitated studies of minute functional details of mechanisms, which finally lead to better understanding of generally similar functions, covered by the multiple developments of Nature as a response to an extreme variety of different conditions. Improved understanding of specific mechanisms, however, has presented new problems at the level of system integration. The importance of the integrative aspect became particularly apparent during an international symposium on 'Mecha- nisms of Systemic Regulation in Lower Vertebrates: Respiration, Circu- lation, Ion Transfer and Metabolism' (organized in 1990 by Norbert Heisler and Johannes Piiper at the Max-Planck-Institut fUr experimen- telle Medizin at Gottingen/Germany).