On the structure of the eye of the swordfish (Xiphias gladius, Lin.) / by Robert Edmond Grant.

Date:
[1827], [©1827]
Catalogue details

Licence: Public Domain Mark

Credit: On the structure of the eye of the swordfish (Xiphias gladius, Lin.) / by Robert Edmond Grant. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    the structure of the eye, belong exclusively to this class of animals; and besides many general peculiarities, the eye presents in the individual species all the variety and irre- gularity which characterize the organs of animals low in the scale, and exhibits a gradual transition to the apparent- ly anomalous eyes of molluscous animals. The broad flat irregular form of the eye, and the quantity of matter inter- posed between the outer coat and the retina, in the sword- fish, closely resemble the appearances presented in the eyes of the Octopus and Loligo. From the great size and simple structure of this organ in fishes, a minute ex- amination of these peculiarities might throw much light on the nature of many parts, the uses of which are still perfectly unknown in the higher orders of animals. The eye of the common swordfish appears not to have been hitherto examined; and I am indebted for the opportunity of making the following observations to Professor Jame- son, who kindly presented me with the two recent eyes, and the whole of the viscera, of the beautiful male specimen of that rare animal, lately taken in the Frith of Forth, and now preserved in the Museum of the University. The eyes of the swordfish are so perfectly lateral in their position, and so flat anteriorly, that that animal can per- ceive objects only with one eye at a time. This is proba- bly another reason, besides those stated above, for the eyes of this fish being usually large. In the specimens I ex- amined, the transverse diameter measured 3 inches, the axis 2] inches, and the entire animal 7 feet 2 inches from the point of the sword to a line drawn between the tips of the tail. The general form of the eye is that of an irregu- lar hemisphere, a little depressed in the direction of the axis, the anterior part corresponding to the flat base of the hemisphere. The eye is circular round the axis, but its sphericity on the back part is very imperfect from the irre-