1897.] EYES OF THE OEDER PRIMATES. 187 



the Macaques, and the Baboons, and a retrogression of type in the 

 pronounced semi-opacity of the optic nerve-tibres in tlie Mangabeys. 



In the family Cebidse we notice at once fi striking difference 

 between the almost Simian type of the Cebinae (which includes 

 the genera Cebus, Lagothrix, and Ateles) from the obviously lower 

 type of eye in the Nyctipithecinae (Dourocoulis and Squirrel 

 Monkeys). The extraordinai'y 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 Cercojiithecus it looks than any of the other genera above 

 mentioned. 



In the Ohrysothrix 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 

 Hapalidse, 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 Avith 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 the 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 I 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. The difference of its eye is too striking to be over- 

 looked, and in my opinion quite overweighs the other differences 

 of structure and habitat. Por the former differences, especially 

 the shape of the ears and face, are very slight compared with the 

 other members of the family ; and as regards the habitat, it is at 



