Now the lens is an epiblastic structure, and the iris is mesoblastic.
The brain is formed out of two epiblastic thickenings which occupy shallow depressions.
The epiblastic invaginations may be recognised in all stages of growth by their chitinous lining and layer of chitinogenous cells, continuous with the similar layers in the external integument.
The epithelium of the stomodæum and proctodæum is derived, however, from two epiblastic involutions at the fore and hind ends of the embryo.
Exoskeletal structures of epiblasticorigin may be developed on both the inner and outer surfaces of the Malpighian layer of the epidermis[1].
There is nearly always a strongly-developed epiblastic exoskeleton which has the form of scales or feathers, and in some cases a dermal exoskeleton is also well developed.
Along the surface of the jaws a thickening of the epiblastic epithelium takes place, giving rise to a ridge, which sinks inwards into the tissue of the jaw, and it is known as the primary enamel organ.
Skeletal structures of epiblastic and hypoblastic origin occur in the Urochordata.
The epiblastic exoskeleton is generally unimportant, the mesoblastic exoskeleton is usually well developed.
Bergh (for Lumbricus and Criodrilus), whose figures show a derivation of the entire nephridium from mesoblast, and an absence of any connexion between successive nephridia by any continuous band, epiblastic or mesoblastic.
Whitman the entire nephridial system (in the leech Clepsine) is formed by the differentiation of a continuous epiblastic band on each side.
Many observers have been led to the conclusion that the pronephric duct is epiblasticin origin, although from its position in the adult, it appears far removed from all epiblastic formations.
Such an animal could go on living and absorbing and digesting food, although itsepiblastic surface was now its digestive internal surface.
On each side of and behind the mouth two whitish masses are visible, which are the epiblastic thickenings which constitute the ganglia of the chelicerae (Pl.
Both figures shew very clearly the difference in character between the cells of the epiblastic mesoblast of the primitive streak, and the more granular cells of the mesoblast derived from the hypoblast.
In the second of them the blastoderm was already imperfectly divided into two layers--a superficial epiblastic layer formed of a single row of cells, and a layer below this several rows deep.
The stomodaeum is formed as an epiblastic pit between the two procephalic lobes (figs.
Where it comes in contact with the wall of the body in front a small epiblasticinvagination arises, which meets and opens into the archenteric sack and forms the permanent mouth.
The proboscis in Prostomum originates as an epiblastic invagination.
The stomodaeum is formed by the usual epiblastic invagination, and becomes the mouth and oesophagus.
The skeletogenous layer of the Actinozoa is probably the morphological homologue of the gelatinous tissue; but the evidence we have is on the whole in favour of the connective-tissue cells it contains being epiblastic in origin.
However this may be, a differentiation into an epiblastic layer of columnar cells and a hypoblastic layer of more rounded cells soon becomes apparent in the body of the embryo.
In Lumbricus and Criodrilus the blastopore remains as the mouth, but in Euaxes a new mouth or rather stomodaeum is formed by an epiblastic invagination between the front end of the two mesoblastic bands.
Such layers when on the outer side of the membrane separating epiblast and hypoblast are undoubtedly epiblastic in origin, but in some cases amongst the Actinozoa they adjoin the hypoblast, and are very probably derived from this layer.
The stomodaeum appears as an epiblastic invagination at the anterior side of the blastoderm, before any trace of the mesenteron is present.
The shell-gland arises as an epiblastic thickening on the posterior and dorsal side.
Paired epiblastic involutions, shewn as pits in the posterior segments in fig.
The intestine takes a transverse direction to the right side of the body, and the anus opens on the right side and close to the foot in the mantle cavity which is formed by an epiblastic invagination in this region.
The figure shews the jaws (mandibles), and close to themepiblastic involutions, which grow into the supra-oesophageal ganglia.
The ventral cords of the trunk are formed as two independent epiblastic thickenings.
Behind the first pair of branchial clefts a second pair is formed during larval life by a second outgrowth of the branchial sack meeting the epiblastic atrial involutions (fig.
The embryo becomes hatched not long after the formation of the oral and atrial openings, and the five epiblastic processes undergo atrophy.
The greater part of the choroid is formed from the mesoblast adjoining the retina, but the epithelium covering its outer wall is of epiblastic origin.
The epithelium of the salivary glands, though these so closely resemble the pancreas, is probably of epiblastic origin, inasmuch as the cavity of the mouth is entirely lined by epiblast.
At this stage the embryo consists of two layers; a columnar hypoblast lining the central cavity or archenteron, and a thinner epiblastic layer.
At the front end of the streak an epiblastic involution appears, which soon becomes extended into a passage open at both extremities, leading obliquely forwards through the epiblast to the space below the hypoblast.
The four hypoblastic spheres next divide, giving rise, together with the eight epiblastic spheres, to sixteen spheres in all; which are nearly uniform in size.
Under the fore-brain appears an epiblasticinvolution giving rise both to the mouth and to the pituitary body.
The upper part of the canal, together with the original nasal pit, is alone lined by olfactory epithelium; the remaining epithelium of the nasal cavity being indifferent epiblastic epithelium.
At the moment of their first separation these spheres are spherical, and arranged in two layers, one of them formed of the four epiblastic spheres, and the other of the four hypoblastic.
If this is not the case it is necessary to admit that there are instances in which a very large portion of the alimentary canal is phylogenetically an epiblastic structure.
Of the eight hypoblastic spheres four soon pass to the centre, while the eight superficial epiblastic spheres form a kind of cup partially enclosing the hypoblastic spheres.
The stomodaeum is formed comparatively late by an epiblastic invagination (fig.
The invagination first commences by an inflection of the epiblast-cells for a small arc on the equatorial line which marks the junction between the epiblasticcells and the yolk-cells (fig.
The ligamentum denticulatum is thus lined on one side by the epiblastic atrial epithelium, and on the other by mesoblastic coelomic epithelium.
While still within the egg-membrane the epiblastic cells become flagellated, and the gastrula rotates within the membrane.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "epiblastic" in a variety of sentences. We hope that you will now be able to make sentences using this word.
