n Mikroskopiese en ultramikroskopiese ondersoek na aspekte van voortplanting by Dendrobaena veneta (Oligochaeta)

Abstract

Reproduction is aimed at maintaining life on earth. When reproduction as a population characteristic is studied, one first has to understand the reproductive processes of the species being studied. The main aim of this study was to determine some of the reproductive structures and processes of D. veneta. All the processes which are mentioned were either studied microscopically and\or ultramicroscopically. The first reproductive structure of D. veneta that was studied was the clitellum. The epithelium of the clitellum is some 2-3 times thicker than that of the rest of the epidermis. Although the clitellum epithelium is thicker, the normal epidermis has the same structure and cells, except for the fine granular cells which only occur in the clitellum. The clitellum epithelium consists of supporting cells, mucous cells and glandular cells overlain by a thin cuticle. Four types of glandular cells were observed: large granular cells; fine granular, proteinaceous cells; orthochromatic and metachromatic mucous cells. The cocoons were also studied. The formation of cocoons is characteristic of all Oligochaeta. The cocoons are formed by the hardening of secretions by the large granular cells in the clitellum. The cocoons have an oval shape, are yellow-green when formed and change colour to red-brown when older. Some cocoons are found in cocoon chambers in the medium in which they are cultured and which protect the cocoon against waterless. The cocoon wall (15 .6-17. lµm thick) consists of several layers (0.95-l.9µm each) which are built up of interwoven fibres. The fibres are built up of microtubules ( ll-l 4nm in diameter).