Book - The Pineal Organ (1940) 14

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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)

Chapter 14 I. Hemichorda

This Class includes Balanoglossus (Fig. 123, Chap. 13, p. 169), a burrowing, marine, worm-like animal of which there are several species, varying in length from 2-3 cm. to i\ metres. No eyes are present in the adult animal, but in the early stages of its development it passes through a stage which is termed the " tornaria " (Fig. 125), which resembles in certain respects the trochophore stage of certain echinoderms, rotifers, annelids,

Fig. 125. — Larval form (Tornaria) of Balanoglossus showing the EyeSpots on the Apical Plate. (After Spengel.)

Annulata, and Brachiopoda, more especially in the presence of an apical plate, bearing a vertical tuft of cilia and eye-spots. The development of Balanoglossus has been described by Spengel, Heider, and Morgan. The last author describes the two eye-cups on the apical plate of the tornaria as being anterior and posterior in position (Fig. 124, A, Chap. 13, p. 170). They consist of a single row of elongated ectodermal cells which are clear and converge towards the centre of the pit ; each is surrounded by a mass of pigment which lies on the outer surface and between the two cups (Fig. 124, B, Chap. 13, p. 170) ; at the base of the plate is a thick layer of nerve-fibres. At a latter stage the apical plate and eyes atrophy and the larva sinks to the bottom and undergoes a metamorphosis whereby it is changed to a worm-like form which leads a burrowing life, like Amphioxus, and has no eyes.

Fig. 126. — Cephalodiscus. (After McIntosh and Harmer.) Colony showing gelatinous investment covering separate zooids. B

grammatic representation of longitudinal

section of a zooid.

an. : anus. op. : operculum. be. 1 : coelom of proboscis. aes. : oesophagus. be.' 1 : coelom of collar. ov. : ovary. be. 3 : coelom of trunk. ovd. : oviduct. int. : intestine. ph. : pharynx. m. : mouth. pp. : proboscis pore. nch. : supposed notochord. ps. : proboscis. ns. : nerve-strand and ganglion cells. stk. : stalk.

Dia

Cephalodiscus is closely related to Balanoglossus, but there is no free-swimming Tornaria, having eye-spots.

Cephalodiscus (Fig. 126) and Rhabdopleura, which lead an inactive, fixed life, being associated in colonies, have no eyes in the mature condition, but Mcintosh has described eye-spots as being present in the polypides of Cephalodiscus.

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 24) Embryology Book - The Pineal Organ (1940) 14. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Pineal_Organ_(1940)_14

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