The requirements of a spherical reference system based on two orthogonal goniometers show a surprising correspondence with the evidence emerging from numerous experimental studies on centrioles and centrosomes: the centrosome, because of the 9-fold symmetry of its centrioles, their orthogonal arrangement and their circumferential polarity, may play the role of an interface, composed by two orth...

Members of the Wnt family have been implicated in a variety of developmental processes including axis formation, patterning of the central nervous system and tissue morphogenesis. Recent studies have shown that a Wnt signalling pathway similar to that involved in the establishment of planar cell polarity in Drosophila regulates convergent extension movements during zebrafish and Xenopus gastrul...

Connor, Demirci and Orhan [5] studied multipliers for bounded statistically convergent sequences. In this paper we get analogous results for I−convergent sequences.

The processes thought to function in Xenopus gastrulation include bottle cell formation, migration of cells on the roof of the blastocoel, and autonomous convergent extension of the circumblastoporal region. A review of recent and classical results shows that only the last accounts for the bulk of the tissue displacement of gastrulation, including spreading of the marginal zone toward the blast...