THAIVOIALS 



459 



The TAPETUM CELLULOSTJM, on the other hand, develops from the 

 ahnost continuous layer of endothelial cells which separates the elastic 

 layer from the choriocapillaris (Sattler, 1876). It is formed of several 

 closely set layers ^ of thin, flat endothelial cells arranged in tiers 

 with mason-like regularity resembling plant tissue rather than animal, 

 each cell being jDacked with rod-like, doubly refracting crystals of an 

 unkno\Mi chemical composition (? lipoid) (the iridocytes of Bruni. 

 1922) (Miirr. 1925-27). Such a tapetum occurs in all Carnivores 

 (except two Viverrines. Cynictis and Suricata) including the Pinnipedes. 

 and also in Prosimians — the lemuroids, Loris. Nycficebus, Galago and 

 Lemur catta. 



Suricate 



Fig. 581.- 



-The Papillated Choroid of the Fruit-bat 

 Pteropvs Polwcephalvs (O'Day). 



(Flyixg Fox) , 



It is interesting that the pigment epithelium of the retina in IMammals is 

 rarely densely pigmented nor is the j^igment migratory. It may contain reflecting 

 material ; this in some fruit -bats (Pteropus) serves as a retinal tapetum in 

 the upper jDart of the fundus, and in the dog is said to augment the effect of the 

 choroidal tapetum. 



VASCULAR CHOROIDAL PAPILLAE are a unicjue phenomenon in the animal 

 world found among the ]\Iegachiroptera — fruit -bats or fl.ying foxes (Pteropus, 

 Epo?nophorus)Ko\mev. 1910-24: Fritsch. 1911; Gerard and Rochon-Duvigneaud, 

 1930) (Fig. 581). These structures which stud the fundus from the ora to the 

 optic disc, form conical mesodermal papilla? each with a vascular core, and on 

 this irregular surface the visual cells of the retina are arranged like trees on a 

 range of hills. Although the retina is entirely avascular all its layers are thus 



^ 4 in the wolverine ; 8-10 in the lion ; 10 in the dog ; up to 35 and of a very 

 large size in the seals. 



Flving fox 



