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Embryology - 19 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 7 The Eyes of Rotifers (Wheel Animalcules)

In tracing the homology of different groups of animals it often appears that although the adult forms of these have undergone marked differentiation along divergent lines, so that they show little resemblance to each other, yet the larval forms are so like that the possibility of the two groups having sprung from a common ancestor is at once apparent. In this respect the study of the larva or trochophore of the rotifers is of the very greatest interest. This trochophore (Fig. 56) is a pear-like structure which in many respects resembles the Tornaria of Balanoglossus (Fig. 124, Chap. 13, p. 170, and Fig. 125, Chap. 14, p. 172). Thus in the trochophore we recognize a pear-shaped organism with the broad end uppermost, having an apical plate bearing a tuft of vertical cilia. This plate has a pair of short tentacles and eye-spots which lie over the nervecentre or ganglion. There are, moreover, usually two circlets of vibratile cilia which surround the body, one lying above or in front of the mouth — preoral — the other below or behind the mouth — postoral. The mouth is placed on one side of the body, namely the ventral aspect, and the anus is at the lower pole or posterior extremity. A pair of tubes, the excretory organs or nephridia, are present and in the female adult an ovarium is connected by an oviduct with the cloaca.

Fig. 56. — Trochophore Larva of a Rotifer showing Apical Plate and Eyespot, OF WHICH THERE ARE USUALLY TWO. (AFTER HATSCHEK.)

An. : anus. nephr. : nephridium.

ap. c. : apical cilia. oes. : oesophagus.

ap. pi. : apical plate. oc. : eye-spot.

int.: intestine. po.or.c: post-oral circlet of cilia.

m. : mouth. pr. or. c. : preoral circlet of cilia.

n. : nerve. st. : stomach.

Taking the adult form of Brachionus rubens as an example, we find that in spite of its minute size there is a high degree of differentiation. As regards the nervous system, a large cerebral ganglion is present at the anterior end of the body which lies above or dorsal to the alimentary canal. Where the cerebral ganglion comes into contact with the bodywall, there is a median eye-spot of small size and red. Three other organs considered to be sensory are known as tactile-rods ; one of these, bearing stiff hair-like organs, projects from the dorsal surface just behind the " wheel " or " trochal disc " ; the other two are paired and situated on the dorsal surface of the glass-like cuticle or " Lorica " ; in a few cases there is in addition to the dorsal ganglion (which is supra-oesophageal in position) a small ventral ganglion which is infra-oesophageal. Compare Fig. 57, showing a longitudinal section of a typical rotifer, with Fig. 68, Chap. 1 1, p. 106, which represents a similar view of Lepidurus. It may be noted that in Lepidurus there are paired lateral eyes in addition to the median eyes.

57. — Diagram of a Rotifer, showing the Relative Positions of the Brain, Median Eye, and other Viscera.

a. : anus. e. : single red eye-spot br. : brain. fl.c. flame cells. c' : pre-oral circlet of cilia. int. intestine. c" : post-oral circlet of cilia. m. : muscles. c.gl.: cement gland. mth. mouth. cl. : cloaca. nph. nephridial tube. cu. : cuticle. ovd. oviduct. cv. : contractile vesicle. ovy. germarium. d. ep. : deric epithelium. ph. pharynx. df. : dorsal feelers. st. : stomach. vt. : vitellarium.

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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)

Cite this page: Hill, M.A. (2024, April 19) Embryology Book - The Pineal Organ (1940) 7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Pineal_Organ_(1940)_7

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