Generation continuity and integration
Russian Agrarian University - Dept. of Entomology, K.A. Timiryazev
Agricultural Academy
ul. Timiryazevskaya, 49, bd8,127550 Moscow
e-mail: info@timacad.ru
Transformation of the cyclic morphoprocesses in Protista toward the terminal-cyclic morphoprocesses in Metazoa had lead to integration of the former's life cycles into the latter's ontogenesis and began to supply the newly emerging ecosystems with the regular income of mortomasses. According to the palintomic hypothesis of A.A. Zakhvatkin, it was the egg that became a means of the metazoan generation continuity, and not the half set of organelles acquired by descendants of a divided maternal cell in Protozoa. Origin of Metazoa and of their ontogenesis was accomplished by hypertrophic distomy and subsequent palintomic division of the protist parental cell, these processes being comparable to the ovogenesis and ovocyte division in the Metazoa. Division process in the most primitive metazoans, Leptolida and Calcarea, retained certains features of its palintomic nature that are clear in the Ctenophora, the latter though specific being most similar in this respect to the sponges and not to the Coelenterata whith whom they were united in the same phylum formerly. The ovogenesis perfection controlled by the maternal organism and leading to an increment of the nucleoplasmic tension due to enrichment of egg with the yolk, promoted the embrionization of development and formation of the egg morphogenetic environment providing for the earlier formation processes without participation of the parental recombined genotypes. With all this, far earlier appearence of symmetry elements of definitive forms in embriogenesis along the ascending trend from the lower Metazoa to the most advanced insects. The unordered correspondence of the polarity axis of egg and the oral-aboral axis of blastula-like larva (1) is replaced by protaxony (2) in which these axes coincide, all formation processes reaching their perfection in the homoquadrant spiral division of annelids, which became a means of ovoplasma segregation. Afterward, a heteroquadrant division and plagiaxony are developed in the course of emergence of bilateral symmetry and embrionization in Clitellata (3), in which principal morphological axes become intersected. With the transition to arthropodes, the spiral division degenerates in a variety of forms (desintegrative variation) and loses its connection with the ovoplasma segregation, which occurs beforehand in the ovogenesis. Connection between parental organism and its progeny becomes more close. Transformation of the ovary into ovariol and vitellogenesis intensification appeared to be of prime importance in the evoluiton of insects. Their eggs became elongated and more or less bilaterally symmetrical. The nucleoplasmic interrelation becomes even more tense, and the enormous yolk store promotes the orientational blastokyneses in the developing embryo. An orthoplagioaxony (4) and lastly orhoaxony (5) emerge in the higher Diptera and Hymenoptera, in which morphological axes of the egg, the embryo, and the larva coincide. This is accomplished by the maximal integration of generations, as far as all germs of the organs of larvae and even imagoes appeared to be preformed in the ovogenesis.
