A.N.Severtsov Institute of Ecology and Evolution, Russian Academy of Science.

M.V.Lomonosov Moscow State University, Biological Faculty, Moscow 119899, Russia.

Abstract

Specialized generator tissues of fish excepting Apteronotidae are of muscle origin. Definitive electric organs of some Apteronotidae develops from motoneurons and obviously are secondary in evolution in contrast to larvae electric organs. Distinctive feature of specialized generator tissues in compare to definitive muscle is co-operative morpho-functional polarity of its erythrocytes. The direction of the polarity is agreed with dorsoventral polarity of the body. All erythrocytes of the given electric organ have unilateral innervation, that allows to summarize cell electric raws. In early stages of muscles innervation has polarity only in embryogenesis when "pioneer" motoneurons come up to its segments (miotoms). Three types of motoneurons can be determined _ rostral (Pro), medianal (Pmi), caudal (Pca) _ in dependence of localization of motoneuron bodies inside nerve tube above each miotom. Pca germinates the first. It selectively innervate only ventrocaudal part of each miotom. The rest two pioneer motoneurons innervate later dorsorostral and dorsomedianal parts of the same miotom. Characters of pioneer motoneurons and electromotoneurons allows to consider that the second ones originates from the first ones. Thus, efferent innervation of electric organs origins from embryonal innervation of skeleton muscle embryo as a result of heterochrony in the rate of development of muscle tissue innervation and the rate of its hystogenesis.