[Analysis of ooplasmic flows and their structural bases during cleavage inPimpla turionellae L. (Hymenoptera) : II. Strain of egg architecture by different acceleration gradients].

In the egg ofPimpla turionellae L., three density gradients are produced by different methods of centrifugation. In spinning, the egg is rotated about its own long axis, so that the lightest egg material is collected in a central column (radial stratification). Flinging parallel to the long axis has been carried out at a short distance from the rotational axis (rotation axis situated immediately adjacent to a long edge of the egg) as well as further from the rotational axis (at a distance of 4.5 cm). A transversal stratification is thereby produced, in which the lightest and the heaviest material are collected at opposite long edges of the egg. The same stratification results from all three methods. From centripetal outward toward centrifugal, a lipid zone, a light yolk zone, a cytoplasm zone poor in yolk granules (basophilic cytoplasmic network), a dense yolk zone and a glycogen zone are formed. The sharpness of separation between the zones in eggs centrifuged during maturation divisions is better than that in eggs spun or flung during cleavage or pre-blastoderm formation. Either development ceases soon after the experiment has taken place or the centrifuged eggs develop into larvae. Half of the eggs flung at short distance or spun about the rotational axis with 10000-12000g are able to develop into embryos. Eggs handled by both of these methods show identical development at increasing accelerations. Eggs flung at greater distance already cease their development after a treatment at 10000g. Malformations or incomplete embryos do not occur in any group of experiments. These findings allow postulation of a system of factors sensitive to accelerations higher than 10000g, which is arranged cylindrically within the egg and which is not connected in any way to the shiftable, light microscopic fractions. This postulated system of factors could have a dynamic function and thereby be an essential component of the primary organization pattern in the egg ofPimpla.Only eggs forming polar caps at opposite ends of the egg within 1.5-2 hours after the experiment will develop into embryos. The polar caps are formed independently of each other. Following too great a stress on the end of the egg oblique to the rotational axis, ooplasm contraction fails to take place. Ooplasmic redistribution has been pursued in life and in section pictures in eggs continuing to and failing to develop. Redistribution combined with a regulated removal of zones is evidently connected with the energid migration. The content of the lipid plasm zone disappears to some extent during redistribution. The posterior part possesses the highest capacity for development in nonviable eggs. It is sometimes able to form a blastoderm independently of the anterior region. A blastoderm is formed only if the posterior part includes the region between 25 and 35% of the egg.