Ultrastructure of the digestive and protonephridial systems of the metacercaria of Euclinostomum multicaecum

The structure of the digestive tract of Euclinostomum multicaecum (Digenea: Euclinostomatidae) is unusual, comprising several main lateral caeca which extend posteriorly and further divide, giving rise to numerous smaller branches which are widely distributed throughout the fluke. These multicaeca presumably promote nutrient absorption during rapid and prolonged feeding directly following excystment. The caecal wall consists of a syncytial gastrodermal epithelium, bearing loop-like lamellae which extend into the lumen and enclose spherical inclusion bodies and presumably also, increase the absorptive surface area. There was no evidence of endo- or exocytosis, nor were lysosomes, phagosomes or residual bodies observed. The gut caeca are supported by a fibrous basal lamina and an underlying layer of muscle fibres, while parenchymal cells occupy much of the extracellular space. The protonephridial system resembles that observed in other digeneans consisting of flame cells and collecting ducts which join to form a bladder that opens externally through a single excretory pore. The syncytial epithelium of the collecting ducts is elevated by numerous lamellae while the basal lamina is highly infolded. The luminal contents of these ducts comprise bar-shaped crystalline structures, lipid droplets and electron-dense inclusion bodies. The excretory system is supported by a network of muscle fibres and parenchymal cells.

A membrane-bound plastid inclusion in the epidermis of leaves of Taraxacum officinale

Epidermal chloroplasts of Taraxacum officinale agg. contain large electron-dense inclusion bodies enclosed by a single membrane. These inclusion bodies were not observed in mesophyll chloroplasts. The origin and functional role of these structures is discussed.

A Strain of Pseudomonas aeruginosa Resistant to a Quaternary Ammonium Compound1

Light and electron microscopy studies were made of Pseudomonas aeruginosa strains which were sensitive and resistant to a quaternary ammonium compound (QAC). The colonies of the sensitive cells on Tryptone Glucose Yeast Extract Agar were granular and homogeneous in consistency. In contrast, the colonies of the resistant strain on the same medium were granular, non-homogenous, and contained numerous dense areas. Morphological observations revealed the resistant cells to be 30% smaller than sensitive cells and non-motile due to loss of polar flagella, a characteristic which was not restored when the organisms were cultured in the absence of QAC for more than 7 months. Electron-dense inclusion bodies were present in resistant cells; they ranged in size from about 0.05 to 0.2 μm in diameter. These bodies, which were not identified, were released intact from lysing cells; as many as 20 per cell were visible.