The blastodic became apparent on day 28 and the blastopore
was visible on some eggs (Fig.
and archenteron were visible in the diminished vegetal half of chlorpyrifos-treated larvae.
In carideans that form a blastoderm, the mesoderm and endoderm rise by subsequent cell ingression and delamination from a small blastopore
located at one of the ends of the longest embryo axis.
Stage II ended when the blastopore
was closed and the optic cups distinguished head and tail regions of the embryo.
2C), is buoyant and pear-shaped, with a central blastopore
. Brachiolariae have two arms in the middle of the larval body (post-oral) and another arm on the pre-oral lobe (Fig.
comprised an ectoderm and endoderm and had a closed blastopore
. Each of the thousands of ectodermal cells bore a single cilium on its outer surface (Fig.
closed on day 15 when the germ ring completely enveloped the yolk.
The resulting blastopore
started as a wide pit, subsequently deepening into the archenteron (Fig.
In Xenopus the epithelium becomes polarized between gastrulation and neurulation; current influx, ranging from 0.1 to several [mu]A/c[m.sup.2], occurs over the entire surface of the embryonic epidermal epithelium; and substantially greater current efflux occurs through the low-resistance path of the blastopore
, the opening to the primitive gut (Robinson and Stump, 1984).
During metamorphosis, the larval anus (the derivative of the blastopore
) closes, and the larval rectum and intestine undergo resorption.
The zoanthella larva (named by van Beneden, 1897) was first described by Semper (1867); this larva is an almost cylindrical planula that has a long, mid-central ciliary band extending from the blastopore
to the anterior pole.
remains open throughout gastrulation and is situated initially in the center of the vegetal pole of the embryo (Fig.