DISSECTION OF
The Platana and the Frog

BY

J. D. F. GILCHRIST, M.A., D.Sc., Ph.D.,

Professor of Zoology in the University of Cape Town,

AND

C. von BONDE, M.A.,

Lecturer in Zoology in the University of Cape Town.

1919.

CAPE TIMES LIMITED, CAPE TOWN.

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PREFACE AND INSTRUCTIONS.

Owing to the fact that some of the types of animals available for the study of Zoology in South Africa differ from those described in text books for students in other countries, it has been found necessary to draw up special directions and diagrams for laboratory use in this country. These are now put in the more convenient form of a text book, which, though intended primarily for the use of the students of the University of Cape Town, may, it is hoped, prove useful to others engaged in the teaching and study of Zoology in South Africa.

The general plan of the course intended to be followed is first an introductory study of a type of vertebrate. The Platana or Clawed Toad, Xenopus lævis, is the most convenient type for this in South Africa and in some respects is more instructive than the Frog.

Xenopus is therefore chiefly dealt with, but Rana can also be used, the differences in this type being indicated in italics. It is recommended that both types be studied where possible.

Only these two types are dealt with here, but may be followed by descriptions of other South African types, such as the South African Crawfish, Dogfish, Earthworm, etc.

It is intended that the student should make drawings of his dissections on the blank page. He should not copy the diagrams, but draw what he actually sees, and be prepared to demonstrate the parts to the teacher.

The instruments required are a large and a small pair of scissors, a large and a small scalpel, moderately fine forceps, a seeker, and pins.

We are indebted to Mr. W. von Bonde, M.A., for the drawing of Figs. 3-5, 7-10.

J. D. F. G.
C. v. B.

Zoological Laboratory,
University of Cape Town,
June, 1919.

THE PLATANA (Xenopus lævis).

THE FROG (Rana fuscigula).

First Day.

External Characters.

1. Make a drawing of the animal viewed from above, showing:—

(a) The nostrils.

(b) The eyes.

(c) The nictitating membrane and a short tentacle beneath the eye. [The tentacle is absent in the Frog.]

(d) The tympanic membrane, which is not shown in the Platana, but is well marked in the Frog.

(e) The opening of the cloaca.

(f) The limbs and their divisions.

(g) The skin with tube-like lines round the body. [In the Frog these lines are not present.]

Fig. 1.—Xenopus lævis and Rana fuscigula.

2. Make an enlarged drawing, about twice the natural size, showing:—

(a) The fore-limb with the digits.

(b) The hind-limb with the digits. The inner three digits have claws. [The claws are absent in the Frog.]

Name the parts of these limbs, and number the digits from within outwards, noting that the first is absent in the fore-limb.

Mouth Cavity.

Open the mouth cavity widely, and make a sketch showing:—

(a) The teeth on the upper jaw.

(b) There are no teeth on the vomer. [In the Frog each vomer is supplied with teeth.]

(c) The internal openings of the nostrils.

(d) The single opening of the Eustachian tubes. [In the Frog there is an opening on each side.]

(e) There is no tongue. [A tongue is present in the Frog.]

(f) The glottis.

(g) The gullet.

Owing to the complexity of the Eustachian tubes and the bony form of the ear cavity, it is not possible to pass a seeker from the Eustachian aperture through the tympanic membrane. [In the Frog the Eustachian tubes are short and straight and permit of this being done.]

Fig. 2.—Mouth cavity of Xenopus and Rana.

Muscular System and Vascular System (Part).

1. Pin the Platana on its back in water, and cut through the