Palaemon lamarrei
1. In the oogonia there are no granules which can be assigned to the category of mitochondria. They appear for the first time in young oocytes in the form of a juxta-nuclear heap of granules or in the form of a horseshoe closely embracing the nuclear membrane. Soon they arrange themselves in the form of a circum-nuclear ring which gradually expands towards the periphery of the oocyte without breaking away from the nuclear membrane. At the same time the marginal mitochondria of the ring grow in size till ultimately they give rise to albuminous yolk, which therefore appears for the first time in the peripheral regions of the cytoplasm (cf. Oniscus, King, 1926, and Rana tigrina, Nath, 1931).
2. A yolk-forming mitochondrium first swells up; but it is still poorly fixed and stained with Bouin-haematoxylin, like the unchanged mitochondria. The process of growth continues and the swelling mitochondria now show an internal differentiation in the form of minute granules or very small vacuoles. Such mitochondria are only slightly better fixed and stained with Bouin-haematoxylin. Gradually they are completely shorn of their lipoidal constituents, condensing at the same time more and more of protein material. Ultimately they give rise to albuminous yolk, sensu stricto, which is fixed and stained excellently in Bouin-haematoxylin.
3. In the earliest oocytes the nucleolus throws out into the cytoplasm deeply basophil pieces which are more or less uniformly dispersed. Soon they disappear. Hereafter the nucleolar extrusions are very minute, but they remain restricted to the perinuclear region. They never wander into the general cytoplasm or at least into its peripheral regions where protein yolk appears for the first time. A direct origin of the yolk granule from the extrusion must, therefore, be ruled out. But the possibility of the extrusions going into solution and thus indirectly contributing towards yolk cannot be eliminated.
4. Although the mitochondria can be easily observed in the fresh cover-slip preparations of young oocytes, the Golgi elements cannot be demonstrated unless the material is osmicated for at least twenty-two hours. Chemically the Golgi elements are lipoidal (fat-like). They are not stainable with neutral red.
5. In the oogonia and the earliest oocytes the Golgi elements exist in the form of vesicles, each vesicle showing a thick osmiophilic cortex and a central osmiophobic area.
6. During oogenesis many vesicles grow enormously in size, store up neutral fats inside them, and give rise to the fatty yolk as in Lithobius, spider, Otostigmus, Luciola, cockroach, Dysdercus, and Ophiocephalus (Nath, and Nath and collaborators), in Oniscus (King), in saw-flies (Gresson), and in Helix (Brambell).
7. The vacuolar system is absent in the prawn and also in the crab.
Paratalphusa spinigera.
8. The Golgi elements of the crab behave exactly like those of the prawn, but the mitochondria, on the other hand, remain inactive and have no visible relationship with yolk formation.
9. In the crab also there are well-marked nucleolar extrusions. As in the prawn a prominent circum-nuclear ring of these granules is established early in oogenesis. But, unlike the prawn, granules from this ring continue to wander into the cytoplasm at the periphery of which they directly grow into the albuminous yolk.
The fine structure produced in cells by primary fixatives 2. Potassium dichromate