FATEMAP OF FERTILISED EGG OF AMPHIOXUS: Conklin in studied the fate map of Amphioxus. In Tunguntung described the egg. Download Citation on ResearchGate | The Embryology of Amphioxus | Although the egg of Amphioxus is much more fluid and less stereotyped than that of. Edmund Beecher Wilson experimented with Amphioxus and Driesch were at the forefront of a movement in experimental embryology called.

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At these lips the entoderm and ectoderm are continuous. Diagram of a median sagittal section through an Amphioxus ovum.

Diagram to show differentiation of primitive segment into muscle plate myotome and cutis plate and relation of myocoel and splanchnocoel. As the embryo continues to grow in length embryolovy notocord too is lengthened by the addition of cells to its caudal end ampihoxus the region of the neurenteric canal.

The invagination, however, is more rapid along the dorsal margin of the plate of macromeres, and as the infolding progresses there is formed a plate of small cells which arise through the more rapid proliferation in the germ ring Fig. Institut zu Wien, Bd. The notochord rolls over the dorsal lip of the blastopore into the interior of the embryo and becomes stretched along the embyology side of the archenteron, forming the mid-dorsal strip of the archenteron roof.

Book – Text-Book of Embryology 4

The somites are block-like in shape and located lateral to the developing notocord and neural tube. The degree of retardation varies in different animals. The concentration toward the dorsal side of the embryo, noted in respect to the notochordal and nervous system material, is also very distinct in the case of the mesodermal mantle.

The simplicity of these first steps, whether it points to primitiveness or not, affords a view of certain fundamental principles of development which makes the study of higher vertebrate forms much easier and renders their formative processes much more intelligible.

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Bonnet, Compare with Fig. The movement of parts of the marginal zone into the interior of the embryo is very different ajphioxus the invagination as seen in Amphioxus.

The sagittal partition between the ccelomic spaces of the two sides then breaks down and each side is in free communication with the other ventral to the gut. Thus, when the outer parts of the cells become narrow, the pigment granules are concentrated in a smaller area, and this concentration of pigment is noticeable on inspection of the embryo viewed from the outside. The closure is not complete in front for some time, and the opening thus left is called the neuropore Fig. At the caudal end the central canal remains in open communication with the archenteron owing to the fact that when the ectoderm grew over the neural plate it also grew over the blastopore.

At the beginning of cleavage three regions can be distinguished in the Amphioxus egg. The position that the spindle assumes is determined by three factors: In later stages it will be seen that the nervous sytem, that complex mechanism for transmitting stimuli from one part of the body to another, is developed from ectoderm. In Amphioxus the neuropore persists until the mouth is formed.


Journal of Morphology, Vol. It has been stated that inflection, or involution, is one of the factors in gastrulation. As the mesoderm moves from the posterior end of the embryo represented by the blastopore toward the anterior end, there remains at the anterior end a region which the mesodermal mantle has not yet reached.

The distinction between gastral and peristomal mesoderm has already been stated, and since mesoderm development is initiated shortly after the gastrula begins to elongate the true gastral portion is relatively short. Division succeeds division in the blastomeres, with the irregularity noted in the preceding paragraph.


The endoderm of the vegetal region passes into the interior of the embryo more or less passively and there comes to lie in the floor of the archenteron. Opposite to this mesodermal embryloogy another crescent is present which becomes presumptive nervous system. He bases his conclusion on nuclear characters.

Book – Text-Book of Embryology 4 – Embryology

In amphioxus blastula is converted into gastrula by the following ways. Amphioxus Greek, “both pointed” referring to their body shapeare commonly called lancelets or small, eel-like animals that spend much of their time buried in sand. The cells of the vegetal pole will divide slowly where as the cells of the animal pole will divide in a quick way. All the cells at a given cleavage thus far have divided at the same time, a fact which is expressed in the term regular cleavage.

The circular opening between the archenteron and the exterior is the blastopore.

Gastrulation in Amphioxus and Amphibians | Embryology

This area of accelerated division then extends in both directions around the margin of the flat pole, forming the germ ring. The blastocoel appears at the 4 celled stage as the cells are round and then do not unite. It is not difficult to see, therefore, that in the higher and more complex animal forms many of the activities of the ectodermal and entodermal derivatives which are correlated with response to external stimuli and with alimentation are made possible by structures elaborated from the mesoderm.

The first cleavage therefore will produce two equal and symmetrical daughter cells, or blastomeres, the first cleavage plane coinciding with the plane of symmetry of the ovum.