Venita F. Allison

The fine structure of spermatogenesis in Hymenolepis diminuta (Cestoda) with a description of the mature spermatozoon

SummaryThe processes of spermatogenesis and spermiogenesis in Hymenolepis diminuta were studied by electron microscopy using improved preparative techniques. Spermatogonia (Type A) are characterized by nuclei 3.79 (±0.17) μm in diameter, dense cytoplasm packed with free ribosomes, and aggregates of mitochondria. After mitoses, certain spermatogonia (Type B) assume syncytial rosettes containing eight nuclei. Primary spermatocytes maintain the rosette syncytium and have large nuclei (4.28±0.24 μm in diameter), smooth endoplasmic reticulum, and polysomes. The secondary spermatocyte is short-lived and is characterized by nuclei (2.0±0.11 μm in diameter) and perinuclear membranous lamellae. The syncytial spermatid cluster contains avoid nuclei which condense and elongate to a final diameter of 0.22±0.04 μm. Once elongated, these nuclei become delimited from the syncytium by invaginations of the plasma membrane. During delimitation, cortical peripheral microtubules arise beneath the spermatozoon plasmalemma and a 9+1 axoneme extends the length of the mature lance-shaped spermatozoon.

Scanning electron microscopy of the eggs of Ascaris lumbricoides, A. suum, Toxocara canis, and T. mystax.

Eggs of Ascaris lumbricoides, A. suum, Toxocara canis, and T. mystax were examined by scanning electron microscopy (SEM). All species under study exhibited pronounced surface ridges. The ridges formed distinctive patterns in T. canis and T. mystax. In the Ascaris species, the ridges are similar except that they are more pronounced in the eggs of A. suum. Operculumlike structures were observed only in Ascaris. Correlation of data from SEM with previously reported transmission electron microscopy suggests that the surface ridges seen in Ascaris eggs are formed by the chitinous layer of the shell.

The fine structure of the cysticercoid of Hymenolepis diminuta

SummaryElectron microscopy of the outer wall of the capsule of the eight-day old Hymenolepis diminuta cysticercoid shows it to be part of a syncytium. The surface cytoplasm is a continuous layer connected by arm-like projections to a nucleated cytoplasm lying beneath the surface. The free surface of the outer cytoplasm is greatly increased by numerous branched microvilli. In addition to the syncytium, a separate cell type is described and evidence is presented for its involvement in the formation of the basement layer and other fibrous components of the cystic wall. The possible functions of branched microvilli are commented upon.

Electron microscopic and microprobe analysis of calciuminduced differentiation of the white mutant (LU887 × LU897) strain of Physarum polycephalum

Differentiation of the white mutant (LU887 x LU897) strain of Physarum polycephalum leading to spherule formation can be induced by CaCl(2) if the concentration in the nutrient medium is increased by 5mM prior to the transfer to a non-nutrient salts medium. All stages previously reported for the typical (M(3)cVII) strain of Physarum polycephalum from microplasmodia to spherules are seen but the mutant lacks the synchrony that the replacement technique induces in the typical strain. X-ray microanalyses locate calcium and phosphorus in granules in mitochondria and in the cytoplasm of specimens fixed without osmium. Mitochondria accumulate calcium-containing granules during early differentiation and appear to be essentially without granules in mature spherules. Mobilization of mitochondrial calcium is implicated in the initiation of differentiation. A longitudinally striated cytoplasmic inclusion is abundant in microplasmodia grown in media that have not been supplemented with additional calcium and is seen more rarely during calcium-induced spherulation. Whether or not this inclusion represents cytoplasmic contractile elements is unknown. The calcium-treated mutant strain, previously considered non-differentiating, may prove to be a good alternate model for the study of factors influencing differentiation. It was employed earlier as a control in studies of strains that readily spherulate in response to routine procedures.

Ultrastructure of the epidermis of a rhabdocoel turbellarian Syndisyrinx sp.

A study of the ultrastructure of the epidermis of Syndisyrinx sp. from the sea urchin Lytechinus variegatus in Jamaican waters reveals several cell types. The anterodorsal surface contains squamous cells, and some basally located cells, at least partially overlapped by the cytoplasm of other cells, within a simple epithelial layer. The squamous and low columnar cells are sparsely ciliated. The pharyngeal epithelium contains simple, tall columnar, highly ciliated cells that border a special type of pharyngeal cell modified for movement of the pharynx. The anteroventral epidermis contains tall, columnar, highly ciliated cells. The epidermis of the dorsomedian, dorsoposterior, ventromedian, and ventroposterior regions contains cells similar to those described within the more anteriorly located epidermis, except for occasional structural modifications which probably reflect the stage of activity of the cell. Both dorsal and ventral surfaces contain light and dark cells. Modified cilia, with a conspicuous expansion of cytoplasm surrounding the shaft just above the surface of the cells, and polymorphic microvilli are described.

A UNICELLULAR ENDOCRINE GLAND IN CESTODES

Unicellular glands are reported from the scolex and anterior neck region of Hymenolepis diminuta and H. nana. Despite positive staining reactions with the presumptive neurosecretory stains, paraldehyde-fuchsin and chrome-alum-hematoxylin, ultrastructurally these glands exhibit many non-neural characteristics. Glandular cell processes are frequently found in close proximity to muscular tissue, particularly in the suckers, suggesting a regulatory role in muscle modulation as a possible function. Two types of putative, neurosecretory cells are reported from the cephalic ganglia and the lateral nerve cords. Neurosecretory regulation of the unicellular endocrine glands is postulated based on the lack of direct innervation of the glands and the frequent close proximity of axons containing putative, neurosecretory granules.

The ultrastructure of cement glands in a rhabdocoel turbellarian Syndisyrinx sp.

The cement glands of a rhabdocoel turbellarian, Syndisyrinx sp., were examined by transmission electron microscopy. The glands appear as large, flattened secretory cells with a cell body and elongate, thin cytoplasmic processes that extend to the female antrum. Presecretory granules are released from the Golgi complex into “filling vesicles” until these vesicles are essentially full before being released into the female antrum.

Electron microscopic observations of an unusual cytoplasmic inclusion in the calcium-starved white mutant (LU887 × LU897) of Physarum polycephalum

Abstract Electron micrographs of Physarum polycephalum microplasmodia (LU887 × LU897) reveal cytoplasmic inclusions that appear “striated” at low magnifications; at higher magnifications these exhibit a structure that we have interpreted as microtubule bundles. The light and dark regions in the inclusions are due to the affinity of some microtubules for osmic acid; these appear to have dense regions while other microtubules remain electron lucent. The diameters of the microtubules are about 32–33nm; the subunits forming the tubule walls measure about 8–9nm in diameter. The diameter measurements are slightly larger than the dimensions assigned to vertebrate microtubules (28nm); however, the diameter of the subunits in the microtubule wall measures about 8–9nm which is essentially the same measurement reported for vertebrate tubulin dimers.