Pseudostome

In all the cases which I have observed, the ciliated bands so characteristic of the pseudembryonic form have made their appearance before the rupture of the vitelline sac; and frequently the pseudembryo has become somewhat reniform, a depressed ciliated patch indicating the position of the pseudostome.

The sarcodic body of the pseudembryo begins to shrink, the pseudostome and the two lower bauds of cilia disappear, and afterwards the two upper bands, and the embryo then becomes fixed to a stone, seaweed, or some other object.

On one side of the body it has formed an arch forwards, its apex nearly touching the second band; and in the wider space thus left between the third band and the fourth, the pseudostome forms a deep involution of the sarcode, keyhole-shaped, richly ciliated, shallow anteriorly and deepening posteriorly into the short curved pseudocele, which merely dips under the fourth band, breaking through immediately behind it as a small round anal aperture.

The opening is via a pseudostome situated on the chamber or at the top of a neck which flares out to form a collar.

It is flattened ventrally and is smooth around the pseudostome area.

Members of the Arcellina (testate amoebae), especially the terrestrial species, are surrounded by resistent tests with only one small pseudostome.