Embryology - 25 Apr 2024 Expand to Translate
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Gladstone RJ. and Wakeley C. The Pineal Organ. (1940) Bailliere, Tindall & Cox, London. PDF

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)

The Pineal Organ - Eyes of Invertebrates

Chapter 5 The Eyes of Flat Worms — Platyhelminthes

In the flat worms, e.g. the fresh-water Planaria or Dendroccelum, there is very evident bilateral symmetry. At the anterior or head-end of the body are a pair of rounded or kidney-shaped black spots — the eyes, or ocelli. They are situated on the dorsal surface of the body and are connected by nerve-fibres with the anterior commissure or cerebral ganglion which joins the right and left longitudinal nerve cords (Fig. 53, B). The eye-spots consist of two or more pigmented epithelial cells which enclose a cup-shaped cavity filled with a clear, refractile substance. Nerve-fibres leave the deep surface of the organ and join the cerebral ganglion. In some marine forms the eyes are multiple and are found on the dorsal aspect of the head, arranged round its anterior margin and sides. In others both marginal and paired eyes are present in the same individual (Fig. 19, p. 25).

Fig. 54. — Ventral Aspect of Larva of Yungia aurantiaca. A — commencement of metamorphosis. B — Metamorphosis almost completed. In A, two pairs of ocelli have appeared in the region occupied by the apical cells of the earlier embryo (Muller's larva). In B, additional pairs of eyespots have appeared in the same region. A pair of temporary eye-spots not shown in the figure also appear on the dorsal aspect of A near the base of the ciliated lobe which overhangs the mouth.

(After Lang, from MacBride.)

In the liver-fluke, Fasciolia hepaticum, which is sometimes found in the larger bile-ducts of the sheep, no eyes are found in the adult form. This is what might be expected during the parasitic phase of the animal's existence, and it is interesting to note that in its free-swimming larval stage, two pigmented eyes are present and that remnants of these eyespots are still found in the sporocyst stage of its existence in the body of a snail.

Eye-spots are also present in the region of the embryonic apical cells on the larva of Yungia aurantiaca (Fig. 51). Two pairs appear first on the ventral aspect, near the median plane ; later, at the period of metamorphosis, other pairs appear farther forward and situated more laterally.

Well-developed paired eyes are present in the Triclad forms of Turbellaria, and an eye-spot is found in the anterior segment of Microstomium, a simple type of Turbellaria which reproduces by an asexual process of budding.

In the tape worms eyes are completely absent, these animals being endoparasitic in all stages of their existence.

Historic Disclaimer - information about historic embryology pages
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)

Cite this page: Hill, M.A. (2024, April 25) Embryology Book - The Pineal Organ (1940) 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Pineal_Organ_(1940)_5

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