Barbara M. MacKinnon

Ultrastructure of the epidermis of adult and embryonic Paravortex species (Turbellaria, Eulecithophora)

The epidermis and associated structures of adult and embryonic Paravortex cardii and Paravortex karlingi, internal parasites of Cerastoderma edule, have been examined using scanning and transmission electron microscopy. The cellular epidermis of adult Paravortex bears cilia and microvilli which differ in number and distribution between P. karlingi and P. cardii. Cellular organelles include mitochondria, lipid bodies, Golgi bodies, and ultrarhabdites. Epidermal nuclei are located in the proximal portion of the cells. The development of the tegument of embryo Paravortex has been described and a possible origin for the embryo capsule is suggested. These findings are discussed in relation to the phylogenetic status of the Turbellaria in relation to other Platyhelminthes and in the functional adaptation of the epidermis for a parasitic mode of life.

The development of the tegument and cercomer of the polycephalic larvae (cercoscolices) of Paricterotaenia paradoxa (Rudolphi, 1802) (Cestoda: Dilepididae) at the ultrastructural level

The development of the tegument and cercomer of Paricterotaenia paradoxa polycephalic larvae was examined using electron microscopy. Larvae are formed by budding from the inner surface of the tegument of the degenerating hexacanth embryo. A new secondary tegument formed around the larvae is probably produced from the original hexacanth sub-tegumental cells. Microvilli covering the surface of young larvae are converted directly into microtriches, as the larvae develop, by addition of electron-dense material to the proximal part of the microvillus. Remnants of the original microvillus are visible at the distal surface of each new microthrix, but they eventually degenerate. The cercomer homologue is represented by scattered follicular cells, bearing microvilli, lying just within the containing cyst wall. The continuity of tegumentary tissue from one developmental stage to the next is discussed.

Heligmosomoides polygyrus: effect of exogenous steroid hormones on egg output in vitro.

The effect of exogenous steroid hormones on the egg output of Heligmosomoides polygyrus (Nematoda: Trichostrongylidae) was examined in vitro. Using worms raised in female mice, it was found that estradiol, testosterone, and cortisone each significantly decreased egg output. Although similar trends were found using H. polygyrus raised in male mice, none of the decreases found was significant. No significant differences were found with ecdysone or progesterone treatments using worms from female or male mice. Treatment of worms with cortisone did not significantly affect retention of eggs within the uterus of H. polygyrus. Titration of the effect of cortisone on egg output indicated that levels of reduction were significant for concentrations of 5.6 x 10(-6) M to 5.6 x 10(-3) M in worms from female mice and for concentrations of 5.6 x 10(-8), x 10(-7), x 10(-5) and x 10(-3) in worms from male mice. Radioisotope labelling experiments showed incorporation of 3H-corticosterone in the nucleus of intestinal cells of H. polygyrus suggesting that its effect on egg production may be via a modulatory effect on the intestinal cells.

A light and electron microscopical investigation of fertilization, chromosome. Behaviour, and early cleavage patterns in Heligmosomoides polygyrus (Nematoda: Trichos-trongyloidea)

Summary Fertilization and early cleavage of the zygote in H. polygyrus have been examined using light and electron microscopy and histochemistry. Fertilization occurs in the anterior uterus where many sperm cluster around each oocyte. The successful spermatozoon lies lengthwise against the oolemma and appears to produce a secretion, believed to originate from the sperm membraneous organelles, which erodes the oolemma. The entire sperm enters the oocyte, the cytoplasmic constituents of the sperm disintegrate, and the condensed nucleus migrates towards the egg nucleus. Just after sperm penetration the egg chromosomes undergo meiosis I, producing a single polar body. The sperm nucleus then enters the egg nucleus and decondenses to produce 6 chromosomes. Cleavage of the zygote is rapidly initiated. Early division of the zygote is usually asynchronous and asymetric. The eggshell is produced immediately following fertilization and is formed primarily from large lipoid inclusions in the oocyte cytoplasm. The cel...