The Multistructured Course - A Preliminary Analysis

An experimental program in which students may enroll in courses for varying amounts of credit, and select course objectives that are in line with their educational goals is described. A preliminary analysis of the results indicates that students tend strongly to approve of the goals of the experiment, have performed well, and, on the whole, react positively to the educational conditions involved. Early evaluation appears to show that some of the techniques commonly used for introductory courses are applicable, and others not very applicable, to education in courses involving upper division and graduate students

Some Observations on Regeneration in Dileptus Anser

One of the most interesting capacities of protozoans is their ability to replace lost parts following injury. Although they are structurally the equivalent of cells they are functional organisms, and a study of their behavior makes it possible to bring together concepts usually applied in the cellular field with those applied in the analysis of whole organisms. The same factors that operate to evoke a particular form in the whole organism must act in a small regenerating piece of a protozoan. Whether these factors are nuclear genes or protoplasmic organization, they act rapidly in the regenerating animal, regulating the form of the piece. Unlike the metazoan material, the morphogenetic activities are not a matter of differential growth rates, but are rather redistribution and reorganization of materials present in the regenerating piece. In this sense the repair of injury inprotozoans more closely resembles cellular differentiation than organogeny

Notes on the Effects of Pretreatment of Spores on the Iodinophile Vacuole of Henneguya exilisl

Spores of Henneguya exilis from the gills of Ictalurus punctatus were exposed to Lugol\u27s solution, Best\u27s carmine, Bauer-Feulgen reaction, and Mitchell\u27s ammoniacal silver nitrate techniques in smears and sections. All of the techniques recognized as specific for glycogen stained the iodinophile vacuole selectively but not specifically, but adjustments to techniques were required. Fresh spores held at room temperatures or chilled for 24 hours were similar insofar as the iodinophile vacuole is concerned, and freezing had little effect. A week or more at room temperature after chilling or freezing for one day resulted in more diffuse staining reactions

Pretreatment of Spores as a Factor in Dimensional Analysis of Two Species of Histozoic Myxosporida

Spores of Henneguya exilis, taken during the summer of 1968 from the gills of Ictalurus punctatus caught in the Des Moines River near Knoxville, Iowa, and of a species of Myxosoma apparently closely related to Myxosoma ovalis, taken from the gills of Carpiodes velifer from the same locality, were subjected to storage at room temperatures, 4° C, and deep freezing. Repeated measurements of spores under different pretreatment showed that the dimensions of the spores and polar capsules remained remarkably stable, as did ratios of the dimensions of spore parts. Abnormalities in the details of spore architecture were seen under conditions under which dimensions remained stable. It is recommended that, wherever possible, unfixed spores be used for measurements, and preserved spores be used for other observations on which species descriptions are to be based

The Myxosporidian Fauna of Some Fresh Water and Marine Fishes

Myxosporidia are highly successful sporozoan parasites of fishes. Although a few species have been described from other cold-blooded vertebrates, fishes are the characteristic hosts and harbor over 90% of the known species. In all localities in which a survey has been undertaken the Myxosporidia have proved to be common. This is equally true of fresh water and marine habitats. Although each species inhabits a particular host organ, the group as a whole have been recovered from the lumina or the tissues of nearly every organ in the body cavity, as well as the muscular, skeletal and nervous tissues and the gills, fins and integument. They may be divided into two categories, the histozoic species which dwell in the tissues of the host, and the coelozoic species, which live in the lumina of various hollow organs. They are never intracellular, and have not been found in the lumen of the alimentary tract

Some Coelozoic Myxosporida from New Zealand Fishes II. on a New Genus of Myxosporida, Auerhachia

Auerbachia, a new genus of Myxosporida, is characterized. Two new species, belonging to this genus, are described. Auerbachia anomald n. sp. is reported from the gall bladder of Genypterus blacodes, and Auerbachia monstrosa n. sp. from the gall bladder of Coelorhynchus australis. All infected hosts were taken by trawler working out of Wellington, New Zealand

A Procedure for Determining the Relative Volume of Mitochondria in Hepatic Cells

About forty years ago Cowdry\u27s monograph on mitochondria appeared evaluating the work of previous investigators, indicating synonymy and, in a sense, bringing the first exploratory phase of the study of these cellular constituents to a close (1). Reasonably specific methods for their demonstration had been devised, and it was possible to have some confidence in the conclusions that the so-called mitochondria of different kinds of cells, despite dissimilarities in size or shape, were comparable cellular parts

Fauna of Testate Amoebae from the Rhytidome of Juglans Nigra

Samples of bark without visible lichen or moss cover were taken from a Juglans nigra located in a city lot in Des Moines, Iowa, remote from water. Euglypha ciliata, E. cuspidata, Microchlamys patella, Centropyxis aerophilus, and two unidentified species of Difflugia were found, ranging from ground level to heights of 35 feet. An estimate of population density, based on a modification of the most probable number count, showed evidence of zonation on the tree surface, with C. aerophilus restricted to near ground level, M. patella occurring approximately evenly up to 35 feet, and E. cuspidata most abundant at moderate heights. Some of the factors related to distribution on the tree surface are discussed

Notes on Iowa Tardigrades

Five species of tardigrades, Macrobiotus areolatus, M. islandicus M. hufelandii, Milnesium tardigradum, and Hypsibius tuberculata are reported from lichens growing on Iowa trees. Factors influencing tardigrade distribution are discussed, especially with reference to the lichen species represented in the samples, and the tree substrate. Hypsibius tuberculata was found to be most abundant about 2 meters above ground level, and to become less abundant below, while the other four species were found to be most abundant near the ground and decline steadily with increasing height. No clear evidence of preference of northern, southern, eastern, or western exposures was found

Some Aspects of Quantitative Histology of the Liver of A-Jax Mice Before and During Tumor Induction with Carbon Tetrachloride

The proportion of the cell populations composed of parenchymal, littoral, and other types of cells is reported for control mice, mice repeatedly anesthetized, mice fed with olive oil repeatedly, and mice fed with carbon tetrachloride and olive oil, showing that the cellular components undergo a marked change when carbon tetrachloride is administered. The proportion of the liver volume occupied by parenchymal cells is found to be relatively stable throughout the period of tumor induction. The nuclear-cytoplasmic ratio of parenchymal cells is found to fall with the aging of control mice and those fed olive oil or anesthetized during the period of the experiment. The nuclear-cytoplasmic ratio is found to fall to a minimal point during the first two weeks of carbon tetrachloride feeding, thereafter gradually rising to normal values for mice of the same age, and eventually rising, after 24 feedings, to a value exceeding that of normal mice of the same age. Between 24 and 30 feedings the nuclear-cytoplasmic ratio undergoes a decrease. The volumes of parenchymal cell nuclei are found to vary with the position in a lobule, the maximal nuclear volumes being found in a region about 100μ to 200μ from the central vein in lobules of average size