[Kinematics and Ultrastructure of Plasmic Factor Regions in the Egg of Wachtliella Persicariae L. (Diptera) : I. The Behaviour of Ooplasmic Partial Systems in the Normal Egg]

The experimental results ofGEYER-DUSZYNSKA (1959), speaking in favour of three ooplasmic factors localized in the pole plasm, in the basophilic oosome material contained therein, as well as in the periplasm of the posterior egg pole ofWachtliella persicariae, suggested to investigate for further factor regions with other technical means. Since ooplasmic factor regions may be indicated by initial regions of morphogenetic development, kinematics were used for in vivo analysis of early embryonic development by means of time-lapse motion pictures. Electron microscopic investigations added to the micro-morphological aspects of plasmic systems within the egg for a better understanding of nature and effectivity of ooplasmic factors.Cleavage nuclei do not move exclusively by means of their spindle activity during anaphase movement. The nuclear envelope of cleavage energides consists of either two unit membranes with pores or of many tube-like as well as membranous elements. The appearence of a complex multi-layered nuclear envelope coincides with the moving phase of energides, an observation which is discussed in relation to the possibility of active nuclear movement. During late preblastoderm the entoplasm contains horse-shoe-shaped and multilobed vitellophagues with dense karyoplasm. With the blastoderm formed, the nuclei may become pycnotic, their membranes fragmenting at the same time. These fragments probably are piled up to form annulated membranes.The pole plasm does not show specific structures apart from the oosome material, contained therein. It is free of yolk material and nearly exclusively consists of ground plasm. The basophilic oosome material within the pole plasm is not surrounded by any membranes. It consists of numerous ribosome-like units and is restricted to the plasm of the future pole cells. The micro structure of the oosome material is preserved at least till the germ band has reached its maximal length.The cell membranes develop by invagination of the oolemma which penetrates into the egg interior. While pole cells and blastoderm cells become tied off, the ground plasm possibly participates in the growing-in process of the cell membranes by developing fibrous differentiations at the terminal extensions of oolemma folds.There is no clear cut limitation between periplasm and entoplasm. The periplasm which is without yolk material, appears rich in ground plasm and does not contain specific ultra structures. During the process of cleavage external ooplasmic regions of the egg are shifted in rhythmical pulsation parallel to its longer axis by a maximum of about 6 % of the entire egg length. Topographic statements of certain areas concerning any anlage therefore are bound to suffer from an adequate lack of exactness. Since comparable shifting processes within the egg plasm probably are common in insects other thanWachtliella, they should be considered as a certain source of error.At 60+-3 % of egg length as measured from its posterior pole, there exists a cleavage centre, an initial region of intravitelline cleavage and of repeated mitotic waves. Adjacent to the middle of the egg follows an initial region of germ band formation (differentiation centre). By their electron microscopic appearance, both developmental centres are not characterized by specific ultra structures. The factor region at the posterior pole exclusively represents an initial region of cell wall formation during superficial cleavage.Other than any experimental marking procedure the technique of time-lapse motion pictures permits to evaluate quantitatively and without artificial interfering the shifting of presumptive segment material during morphogenetic movements of the germ band. The embryonic material of the blastoderm at the egg equator is used for building up the first abdominal segment. The prothoracal and mesothoracal material at about 60% of the egg length stays in site when the germ band becomes extended lengthwise. Closely behind the differentiation centre there is a region of maximal extension as well as of shortening of the germ band. No proliferous growth of segments (segment formation zone) has been found.