Oogenesis in the Desert Snail Eremina desertorum with Special Reference to Vitellogenesis

Abstract

1. The histological structure of the ovotestis is briefly described. 2. The germinal epithelium gives rise to both categories of germ cells (male and female) as well as to the nurse cells. 3. During the differentiation of the germinal epithelial cell towards the germ line, it passes through a certain stage, ‘the progerminative indifferent stage’, before it is polarized either towards the male or female line. 4. A detailed description of the mode of differentiation of the progerminative indifferent cell into the earliest female element is given. 5. Mitotic multiplication of the early female elements never occurs. Nevertheless the diploid chromosome complement is represented by prochromosomes. 6. During the oocytic meiotic prophases, parasynaptic conjugation of the chromosomes is quickly followed by relational coiling of the synaptic mates, and the formation of the strepsitene double spirals. 7. The strepsitene double spirals give rise to the diplotene bivalents of the haploid count 28. 8. The steps of chromatin diffusion that lead to the construction of the typical oocytic germinal vesicle are described. 9. Changes in size, number, and stainability of nucleoli during oocytic growth are recorded. Extrusion of basiphil material from the nucleolus into the ooplasm is highly probable. 10. The mitochondrial granules at the beginning of the period of active oocytic growth form a huge zone to one side of the nucleus. Later they increase in number and widely scatter in the ooplasm. It is held (in favour of Harvey's view, 1929 and 1931) that mitochondria are probably concerned in the chemical synthesis of yolk from raw material provided in the ooplasm. 11. The Golgi bodies in oocytes are in the form of rods and not vesicular. In the early oocyte they form a group to one side of the nucleus. Eventually they disperse in the ooplasm either singly or in small typical complexes. Each of the latter is constituted of a few rods arranged end to end as if on the perimeter of an irregular circle. 12. The earliest yolk spheres (largely proteid) appear in the interior of the Golgi complexes or on the concave sides of the separate Golgi rods. 13. The Golgi rods become severed from the yolk spheres and migrate mainly towards the periphery of the oocyte where they collect in clumps. 14. The elements of the Golgi clumps become loaded with an unsaturated free fat. The original Golgi rod always preserves its identity and never transforms itself into fat.