[Cleavage and gastrulation in Microsomacanthus paramicrosoma (Cyclophyllidea, Cestoda)].

On the basis of hystological studies a description of fission and gastrulation in Microsomacanthus paramicrosoma (gasowska, 1931) is given. Eggs lacking morphological characters of polarity and symmetry display features of duet and spiral fission characteristic of lower groups of Turbellaria. Serial sections (5 mcm thick) have shown that the fission ends in the formation of coeloblastula consisting of 26 +/- 3 cells. Gastrulation is expressed in immigration into blastocoel of two micromeres which later degenerate. These micromeres are homologous to entomesodermal micromeres of other Platodes. Blastocoel disappears as a result of local reproduction of ectodermal cells that is regarded as an anlage of ectomesenchyma. Ectoderm and mesenchyma are not morphologically separated from each other.