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D E PHILPOTT

Publications and source records attributed to D E PHILPOTT.

At least 19 recordsLinked to original sources
PubMed1960

Electron microscopy of the centrifuged sea urchin egg, with a note on the structure of the ground cytoplasm.

Centrifuged, unfertilized eggs of the sea urchin, Arbacia punctulata, have been studied with the electron microscope. Subcellular particles were stratified by centrifuging living cells, known to be normally fertilizable, for five minutes at 3,000 g. The layered subcellular particles, including cortical granules, 16 mmicro RNP particles, pigment, yolk, mitochondria, and oil droplets, possess characteristic ultrastructural features by which they may be identified in situ. The clear zone contains 16 mmicro particles, most of them freely dispersed, scattered mitochondria, and a few composite structures made up of annulate lamellae in parallel layers or in association with dense, spherical aggregates of the RNP particles. Free 16 mmicro particles are found, in addition, throughout the cell, in the interstices between the stratified larger particles. They show a tendency to form ramifying aggregates resulting from certain types of injury to the cell. A few vesicular structures, found mainly in the clear zone, have attached RNP particles, and appear to be related to the ER of tissue cells. Other vesicles, bounded by smooth membranes, are found throughout the cell. These are extremely variable in size, number, and distribution; their total number appears to depend upon conditions of fixation. It is suggested that limited formation of such structures is a normal property of the ground cytoplasm in this cell, but that fixed cells with very large numbers of smooth surfaced vesicles have produced the latter as a response to chemical injury. A model of the ground cytoplasm is proposed whose aim is to reconcile the rheological behavior of the living cell with the ultrastructural features observed.

Animals↗
PubMed1957

The microstructure of the compound eyes of insects.

The apposition eyes of two diurnal insects, Sarcophaga bullata (Diptera) and Anax junius (Odonata), have been examined with the electron microscope. In the latter case only the rhabdom is described. The rhabdom of the fly consists of a central matrix and seven rhabdomeres, one for each retinula cell. The rhabdomeres show an ordered internal structure built up of transverse tubes, hexagonal in cross-section. These slender compartments running the width of the rhabdomere are 370 A in diameter. After fixation with osmium tetroxide the walls of the compartments are more electron dense than the interiors. The retinula cells contain mitochondria, and pigment granules smaller than those found in the pigment cells. These granules tend to cluster close behind the membranes which separate the retinula cells from their rhabdomeres. The rhabdom of the dragonfly is a single structure which appears to be composed of three fused "rhabdomeres," each similar to a rhabdomere of Sarcophaga. Reasons are given for believing that the rhabdom may be the site of photoreception, as well as the organ for analyzing plane-polarized light, as suggested by other workers.

Animals↗
PubMed1957

Electron microscope studies of early stages of sperm penetration in Hydroides hexagonus (annelida) and Saccoglossus kowalevskii (enteropneusta).

1. The early events of sperm entry in Saccoglossus and Hydroides are described and examined in relation to present knowledge of the acrosome reaction and of egg membrane lysins. In Saccoglossus and several other species these events occur in two phases. First. The acrosome filament of the spermatozoön spans the egg membrane barriers, reaches the reactive egg protoplasm, and causes the egg to begin its fertilization reaction. Second. The filament and its connected sperm head move through the egg membrane barriers and enter the egg proper. The first phase is completed in a matter of seconds but the second phase usually requires several minutes. 2. The peripheral areas of the eggs of the two species differ as seen in sections. In Hydroides, but not in Saccoglossus, the vitelline membrane is bounded by a distinct outer border layer of small concentrically differentiated bodies and penetrated by microvilli from the egg. 3. The acrosome filament, seen in the living condition as a delicate thread in Hydroides and as an exceedingly tenuous thread in Saccoglossus, appears to be tubular in both species when seen in electron micrographs of thin sections. 4. The acrosomal region of Hydroides appears to consist of two components-a peripheral one, which may collapse during the acrosome reaction, and a central one related to the acrosome filament. 5. Deliberately induced polyspermic material was used to increase the probability of finding examples of sperm penetration in thin sections. 6. As seen in sections, areas of low electron density, interpreted as spaces or pits from which the material of the membrane is absent, surround the attached or penetrating spermatozoa. (a) In Hydroides the spaces vary greatly in many characteristics including shape, position in the membrane, and size with relation to the enclosed sperm head. In one specimen a portion of the membrane is missing from border to border; no spermatozoön is seen but immediately beneath the space is the apex of a fertilization cone. (b) In every case in which a determination could be made, the spermatozoön in the membrane has undergone its acrosome reaction. (c) In Saccoglossus some pits are found with which several spermatozoa are associated. Generally, where the spermatozoa are more numerous the pit is larger. (d) Pits similar to those seen in Saccoglossus sections are observed in living eggs. They remain in Membrane I after sperm entry. (e) From the above and other considerations it is suggested that the pits and spaces are formed by local action of a lysin or lysins emanating from the individual spermatozoön at the site of sperm entry. 7. It is considered that the suggested lysin would participate in sperm entry by eroding the membrane barrier in the vicinity of the sperm head, thus permitting the sperm head to pass through the membrane. Since the acrosome filament much earlier stimulates the egg's initial fertilization response, this lysin would facilitate the second phase of the early events of sperm entry.

Acrosome↗