THE TAPETUM CELLULOSUM 



233 



perfectly known, ophthalmologically speaking. Such forms as the moon- 

 eye (Hiodon) probably have tapeta of some sort, possibly tapeta fibrosa; 

 but they have not yet been studied. 



At least two or three of the marsupials have produced tapeta fibrosa. 

 Those of the elephants and whales, however, may be genetically related 

 to the tapetum of the ungulates, of which both groups are sometimes 

 considered to be remote kin. In the broadest sense of the term, the 

 elephants are ungulates. The whale tapetum differs from that of a 

 hoofed creature only in being thicker and more extensive in area, though 

 it is usually restricted to the superior half of the retina. 



The excellent tapetum fibrosum of Aotus (= Nyctipithecus) , whose 



Fig. 93 — ^Tapeta lucida in surface view. 



a, fundus of carnivore (dog; right eye), showing characteristic shape of tapetum cellulosum 

 (hatched) and usual location of disc (stippled); the tapetum fibrosum in ungulates has 

 about the same extent, but is more rounded dorsally and tends toward a semicircle in shape. 

 Redrawn from Preusse. b, single cell from tapetum cellulosum of domestic cat, showing 

 rodlets of reflective material. Redrawn from Murr. c, shape and extent of tapetum of the 

 common opossum; the drawing could serve fairly well to represent the whales and the one 

 tapetalized rodent, Cuniculus paca; but the tapeta of seals are even more extensive. 



eyeshine is reported to be more brilliant than that of the cat, represents 

 another independent concoction of the fibrosum type. These douroucoulis 

 or night-monkeys are the only nocturnal Simiae — thus, the only nocturnal 

 New World primates — and the tapeta of the Prosimiae belong to quite 

 another category: 



The Tapetum Cellulosum — Besides the tapetum fibrosum, another 

 equally widespread chorioidal type is the tapetum cellulosum. The noc- 

 turnal prosimians (whose eyeshine is especially vivid) , all but two species 

 of the great order Carnivora, and all of their close relatives the seals, 

 have been found to possess this more complex type. The glorious eye- 



