A morphological type of Sarcocystis cysts found in one of two examined great black-backed gull, Larus marinus (Linnaeus) (Laridae), is considered to represent a new species for which the name Sarcocystis lari sp. n. is proposed and its description is provided. The cysts are ribbon-shaped, very long (the largest fragment found was 6 mm long) and relatively narrow (up to 75 μm). Under a light microscope the cyst wall reaches up to 1 μm and seems to be smooth. Using a computerized image analysis system, knolls, which resemble protrusions on the wall surface, are visible. Lancet-shaped cystozoites measure in average 6.9 × 1.4 μm (range 6.3-7.9 μm × 1.2-1.5 μm) in length. Observed using Transmission electron microscopy (TEM), the cyst wall is wavy and measures up to 1.2 μm in thickness. The parasitophorous vacuolar membrane has regularly arranged small invaginations. Cyst content is divided into large chambers by septa. Sarcocystis lari sp. n. has type-1 tissue cyst wall and is morphologically indistinguishable from other bird Sarcocystis species characterized by the same type of the wall. On the basis of 18S rRNA gene, 28S rRNA gene and ITS-1 region sequences, S. lari is a genetically distinct species, being most closely related to avian Sarcocystis species whose definitive hosts are predatory birds.
The goal of the Hipparcos mission is an ambitious one - the creation of an astrometric catalogue of some 120 000 stars,
with an unprecedented precision on each of their five astrometric parameters. With these data, the astronomical community will be provided with fresh and dramatic insights into many aspects of this fundamental branch of science. Astrometrists will have at their disposal a vast quantity of accurate and homogeneous data which can be used to improve upon the present knowledge of the optical reference frame, and which will provide a dense reference system for past and future ground-based observations. Astrophysicists will be provided with parallaxes and proper motions of not only a highly accurate but also a remarkably homogeneous nature. Important
by-products of the measurements will be a systematic search for binary and multiple star systems, and about 100 high-precision photometric measurements for each star distributed over the
2.5-year mission lifetime. This paper provides an outline of the principals of the satellite operation, the predicted accuracy status,
an overview of the Input Catalogue contents, and a summary of the steps constituting the data reduction. Special emphasis is given to the activities ensuring that a single Hipparcos Catalogue emerges from the parallel work of the two data analysis teams.