Embryology of Temnocephala novæ-zealandiæ Haswell

Abstract

The egg of Temnocephala novæ-zealandiæ consists of a zygote surrounded by polyhedral-shaped yolk cells. First cleavage results in the formation of a macromere and a micromere. The macromere divides into another macromere and a micromere, and after this three-celled stage each cell divides evenly and repeatedly, producing a large number of macromeres and micromeres. These constitute the blastoderm and are centrally situated in the yolk mass, which now is a syncytium (Y). When fully formed, the blastoderm is also syncytial in nature, thus necessitating the description of its component cells as macronuclei (Ma) and micronuclei (Mi). Two germinal layers are recognized. The macronuclei give rise to the oesophagus, intestine, reproductive organs and excretory apparatus and are regarded as belonging to the hypoblast (Hp). The micronuclei give rise to the nervous system, pharynx and body-wall and are regarded as epiblastic (Ep).