Pre-existing Nucleus Research Articles

Fusion of Spermatozoa with Embryonic Cells and Somatic Cells in the Sea Urchin: (fertilization/re-fertilization/acrosome reaction/sea urchin).

Spermatozoa can enter the separated blastomeres of 8- and 16-cell stage embryos, the cells of blastulae and even somatic cells of the oesophagus wall of an adult sea urchin, under certain conditions. In the presence of egg jelly solution, the rate of entrance of spermatozoa is remarkably increased. In the case of the blastomere of 8-cell stage embryos, characteristic cytoplasmic protrusions are formed at the sites of sperm entry, in succession to the formation of the cytoplasmic bulge. These protrusions elongate until 4 min after insemination, and then they retract gradually. The nucleus of penetrated sperm swells and decondenses to form a pronucleus. In most cases, the pronucleus seems to fuse with the preexisting diploid nucleus of the blastomere. When the dissociated oesophagus cells were inseminated, a certain type of the cells was found to fuse with spermatozoa, although the percentage of fused cells was very low.

The stability of gaseous nuclei at liquid-solid interfaces

A free energy analysis is used to investigate the stability of gas-vapor nuclei which are trapped in solid surface cavities. The cavities are axisymmetric but otherwise of arbitrary geometry. For a uniform temperature, it is shown that a pre-existing nucleus begins to grow spontaneously when the radius of curvature of the liquid-gas interface reaches a local minimum value. For a range of contact angles this condition implies that the liquid-gas interface is hemispherical. Results are presented for a cavity of specific geometry—the conical cavity.

The dynamics of the nucleus of M31

Self-consistent dynamic models of the M31 nucleus were constructed which satisfy Stratoscope II and ground-based photometry, as well as ground-based velocity dispersion measurements. Two models designed to yield the highest and lowest mass-to-light ratios (M/L) consistent with observations are concentrated on. It is found that self-consistent static models of the M31 nucleus can be constructed with a nuclear mass-to-blue magnitude ratio between 0 and 50, and that it is very difficult to construct high M/L models with plausible evolutionary histories. The low values of M/L that were found suggest that the nucleus must be composed of stars on nearly radial orbits whose apocenters lie well outside the observable part of the nucleus. Such nuclei may be formed either during core collapse of a preexisting dense nucleus or by orbital decay of globular clusters in a triaxial bulge.

Experimental formation and significance of etch patterns on detrital garnets

The patterns found on the surfaces of etched detrilal garnets are formed by facets that resemble a series of elongated overlapping sharp-edged rectangular or rhombohedral building blocks, mammilla, or rounded hummocks that are gradational to facets and rhombohedral or triangular pits.Opinion on the origin of these surface features is split between those who have suggested that they are due to etching and those who believe they are due to overgrowth. In order to resolve this controversy, crushed garnets were subjected to three sets of experiments. The first involved leaching the crushed garnets in various strengths of acid (HF) and alkaline (NaOH) solutions. The second involved thin-sectioning of naturally etched garnets to determine if a nucleus could be seen under a petrographic microscope and the third involved electron microprobe and SEM X-ray analyses across cut sections of naturally facetted garnets to determine compositional variations through individual grains and between grains from a single sample.The results of the first set of experiments showed that etching starts immediately in all concentrations of HF and that within the first 24 h, facets, mammilla, and pits are visible on the surface of the grains removed from a 40% solution of HF. The second and third sets of experiments showed that, first, the garnets are chemically homogeneous from the inside to the outside of the grains and, second, that there is a wide variation in the chemical composition of the edges of garnets from a single sample.The chemical homogeneity of the garnets demonstrates that the surface patterns did not develop from growth over a pre-existing nucleus. This observation, and the variation in chemical composition of the edges of garnets within a single sample, indicate that the surface patterns on the detrital garnets are the result of etching by intrastratal solutions.