Observations on the ophthalmoscopic appearances of the eyes of the order of primates / by G. Lindsay Johnson.

  • George Lindsay Johnson
Date:
[1897]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the ophthalmoscopic appearances of the eyes of the order of primates / by G. Lindsay Johnson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    1897.] the Macaques, and the Baboons, and a retrogression of type in tlie pronounced semi-opacity of the optic nerve-fibres in the Mangabeys. in the family Cebidaj we notice at once a striking diiference between the almost Simian type of the Cebiuas (which includes the genera Cehas, Lagothruv, and Aides) from the obviously lower type of eye in the Nyctipithecinte (Dourocoulis and Squirrel Monkeys). The extraordinary development and prominence of the choroidal vessels and the peculiar pigmented background so characteristic of the Lemurs distinguish the latter at once. _ Only in the Howlers do we get an approximation to a Cercopitliecus. But if we examine a Howler we notice at once how much more like a Cercojtitheeiis it looks than any of the other genera above mentioned. In tlie C'hnjsotJiriv we find a most peculiar change at the macula. This is surrounded by a remarkable rainbow-coloured ring (see Plate IV.). Now this rainbow ring is the characteristic of the Hapalidfe, occurring in every one of that family that I have ex- amined, only differing from that seen in the Chrysothrix in being a smooth ring instead of a ring made up of extremely short and thick radiating streaks. This ring is the first indication of the gorgeous colours seen in the background of the eyes of the Galagos, the Loris, and the Aye-Aye. When we then come to the Lemurs we do not find a single animal which possesses even a trace of a macula or ring, and the discs are all round. Instead of being pink they are quite white, as if atrophied, and the fundus is of a peculiar brown or greyish- brown colour stippled at regular intervals with large dots (see Plate v.). The moment we descend below the true Lemurs the entire fundus changes : instead of being brown it assumes an intensely dazzling golden yellow. The Galagos, Lorises, and Aye-Aye are all nocturnal animals, and that is perhaps one reason why the fundus is of such a brilliant golden-yellow colour. In the Galagos the disc is nearly black; the fundus is a rich golden yellow with a tinge of green and covered everywhere with minute black or brown stellate dots. These stellate dots are peculiar to the Galagos. If we examine the eyes of the Galagos we find they are nearly alike ; and when we examine the Lemurs we likewise see a family likeness, but fundamentally different in type from the former. Among thp. latter, however, there is one exception, its fundus is identical with that of the Galagos and yet it is known as Coquerel's Lemur (see Plate VI.). Now 1 have examined this animal most carefully, and I am convinced it is a Galago and not a Lemur, notwithstanding the disproportionate size of the tarsus, which, however, is not much larger than those of the Lemurs. I'he difference of its exe is too striking to be over- looked, and in my opinion quite overweighs the other differences of structure and habitat. For the former differences, especially the shape of the ears and face, are veiy slight compared with the other members of the family; and as regards the habitat, it is at [5]