Korschelt considers that all the chief elements of the egg-tubes, viz. egg, nutritive, and epithelial cells, arise by a direct transformation of the elements of the terminal chamber, and that the last may be traced to the indifferent elements of the terminal thread, the elements in question originating from the nuclear elements by a breaking down of the syncytium (or masses of protoplasm with nuclei scattered through it) composing it (Fig. 475).
The latest work is that of Wielowiejski (Zoologische Anzeiger, ix, 1886, p. 132), whose observations are based on a study of the ovarian tubes and the growing eggs of the Hemiptera (Pyrrhocoris), the Coleoptera (Telephorus, Saperda, Cetonia and Melolontha, Carabidæ, and Hydradephaga), etc.
Wielowiejski divides the ovaries of insects into three groups:—
1. Comprising such ovaries in the ends of whose egg-tubes (terminal filament) the embryonal cells in the early stages are accumulated, and are transformed into egg-, yolk-, and epithelial cells respectively. (Ovaries of Orthoptera, geodephagous and hydradephagous Coleoptera, Lepidoptera, Diptera, and Hymenoptera).
2. Comprising ovaries whose ends above the egg-cells and egg-germs (Eianlagen) possess throughout life a more or less voluminous solid accumulation of cells (terminal chamber), but which stand in no close relation with the first. (Ovaries of Coleoptera, with the exception of the Geodephaga and Hydradephaga, and Aphidæ in part.)
Fig. 474.—Various types of ovarian tubes, diagrammatic: A, ovarian tube without nutritive cells. B, egg-tube with alternating nutritive and egg-compartments. C, ovarian tubes in which the terminal chamber (ek) is developed into a nutritive chamber, with which the developing eggs remain connected by means of threads (ds); ef, terminal filaments; efa, egg compartments or chambers; fe, follicle epithelium; df, yolk-chambers.—After Lang (C from Claus).
Fig. 475.—Upper portion of the ovary in Forficula, showing eggs and nurse-cells; below, a portion of the nearly ripe egg (e) showing deutoplasm-spheres and germinal vesicle (gv). Above it lies the nurse-cell (n), with its enormous branching nucleus. Two successively younger stages of egg and nurse-cell are shown above.—After Korschelt, from Wilson.
