Blastopore Sentence Examples

Formation of archenteron and blastopore may, however, be deferred till a later stage (actinula or after).

The preconchylian invagination or shell-gland is formed in the embryo behind the velum, on the surface opposite the blastopore.

C, Diblastula of an Opisthobranch (Polycera) with elongated blastopore oi.

Then the large cells recommence the process of division and sink into the hollow of the sphere, leaving an elongated groove, the blastopore, on the surface.

The blastopore now closes along the middle part of its course, which coincides z s FIG.

One end of the blastopore becomes nearly closed, and an ingrowth of ectoderm takes place around it to form the stomodaeum or fore-gut and mouth.

The other extreme end closes, but the invaginated endoderm cells remain in continuity with this extremity of the blastopore, and form the " rectal peduncle " or " pedicle of invagination " of Lankester, although the endoderm cells retain no contact with the middle region of the now closed-up blastopore.

When the middle and hinder regions of the blastopore are closing in, an equatorial ridge of ciliated cells is formed, converting the embryo into a typical trochosphere.

It has usually been regarded as representing both endoderm and mesoderm, and the groove which usually leads to its formation has been compared to the abnormally elongated blastopore of a typical gastrula.

It is at times sacculated, but its chief interest is that, as Lebedinsky 1 has shown, the tip of the caecum in embryonic life opens to the exterior as the blastopore.

In this stage the body is composed of two layers, ectoderm (d) externally, and endoderm (c) internally, surrounding a central cavity, the archenteron (b), which communicates with the exterior by a pore (a), the blastopore.

They surround a region which is termed the peristome, and which contains in the centre the blastopore, which becomes the adult mouth.

In the anthopolyp the blastopore is carried inwards by an in-pushing of the body-wall of the region of the peristome, so that the adult mouth is an opening leading into a short ectodermal oesophagus or stomodaeum, at the bottom of which is the blastopore.

Gastrulation takes place by epiboly, and the stomodaeum (oral invagination - mastax pharynx) takes place in two stages of the region of the closed blastopore.

The blastopore has open to the exterior by two simple closed.

The little mass of hypoblast or enteric cell-mass now enlarges, but remains connected with the cicatrix of the blastopore or orifice of invagination by a stalk, the rectal peduncle.

The orifice of invagination (blastopore) narrows, and we now have a two-cell-layered sac - the gastrula.

The cavity communicating with the blastopore and lined by the endoderm is the archenteron.

The blastopore, together with the whole embryo, now elongates.

The blastopore then closes along the middle portion of its extent, which corresponds with the later developed foot.

A, First four cells resulting from bl, Blastopore.

Segmentation is total and at first regular, and is followed by invagination, the blastopore passing to the position of the future mouth.

The embryo now consists of two layers of cells, epiblast and hypoblast, surrounding a cavity, the archenteron, which opens to the exterior by the orifice of invagination or blastopore.

After invagination is completed, the embryo begins to elongate, the blastopore becomes narrower, and the dorsal wall of the gastrula loses its convexity, and becomes flattened to form the dorsal plate, the outer layer of which is the primordium of the neurochord and the inner layer the primordium of the notochord.

An important fact to note is that the blastopore is included in this overgrowth of epiblast, so that the neural tube remains for some time in open communication with the archenteron by means of a posterior neurenteric canal.

It is thus possible that the neurenteric canal is due to the conjunction of a posterior neuropore with the blastopore, i.e.

The blastopore generally occupies a position corresponding to the posterior end of the body.

The mesoblast of the cephalic (naupliar) region probably arises in connexion with the lips of the blastopore and consists of loosely-connected cells or mesenchyme.

The gastrula thus formed has a large blastopore, which is at first posterior but afterwards gradually moves towards the anterior end of the ventral surface.

The segmentation is peculiar, and leads to the formation of a solid gastrula, consisting of a cortex of ectoderm nuclei surrounding a central endodermal mass, which is exposed at one point - the blastopore.

The hind end of embryos B, C, D is uppermost in the figures, the primitive streak is the white patch behind the blastopore.

B, Older gastrula stage, ventral view, showing elongated blastopore and primitive streak.

C, Ventral view of embryo with three pairs of mesoblastic somites, dumb-bell shaped blastopore and primitive s t r e a k.

D, Ventral view of embryo, in which the blastopore has completely closed in its middle portion.

Ova large, with much yolk and thick membrane, like those of Australasian species; embryos with slit-like blastopore and of very different ages in the same uterus, probably born all the year round.

Segmentation is complete, a gastrula is formed, the blastopore closes, the archenteron gives off two coelomic sacs which, as far as is known, are unaffected by the super ficial segmentation of the body that divides the larva into three segments.

The internal structural differences are even more characteristic. In the hydropolyp the blastopore of the embryo forms the adult mouth situated at the extremity of the hypostome, and the ectoderm and FIG.