474 



Dr. Gr. L. Johnson. Contributions to the 



received from the Society for the last five years during which inves- 

 tigations on Electric Eadiation have been in progress at the Presidency 

 College. I may say that the difficulties have been very numerous and 

 disheartening, and that without this encouragement the work which it 

 has been my good fortune to carry out would in all probability have 

 remained unaccomplished. The Government of Bengal has also been 

 pleased to evince a generous interest in these investigations. My 

 assistant, Mr. Jagadindu Eay, and my pupils, Messrs. P. K. Sen, B.A., 

 and B. C. Sen, B.A., have rendered me active assistance.] 



" Contributions to the Comparative Anatomy of the Mammalian 

 Eye, chiefly based on Ophthalmoscopic Examination." By 

 G-EOKGE Lindsay Johnson, M.D., F.E.C.S. Communicated 

 by Hans Gadow, F.E.S. Eeceived May 7, — Eead May 17, 

 1900. 



(Abstract.) 



Observations were made on the eye of the living animal, 181 dif- 

 ferent species being examined, and frequently several individuals of the 

 same species. The species comprise representatives of all the Mam- 

 malian orders except the Cetacea and Sirenia. 



The conclusions arrived at can be summed up as follows : — 



The colour of the Fundus oculi in animals devoid of a Tapetum is 

 mainly determined by reflection from the choroidal pigment ; in those 

 with a Tapetum cellulosum (Carnivores) by the colour of the retinal 

 pigment ; in those with a Tapetum fibrosum (Ungulates) by the 

 structural colour of the Tapetum modified by the colour of the retinal 

 pigment. All the animals examined may be classed under three types 

 — red, yellow, and green. 



The vascularisation of the retina can be summarised as follows : — 



1. Indirect supply by means of osmosis from the vessels of neigh- 

 bouring parts. A. Hyaloid supply. (ci) The corpus vitreum is 

 nourished by a processus falciformis, the hyaloid vessels lying well 

 inside the corpus vitreum (Elasmobranchs). (h) The hyaloid vessels 

 spread over the surface of the corpus vitreum, being in consequence in 

 the immediate vicinity of the retina {e.g.^ holosteus and many tele- 

 osteous fishes). Hereto belong also the Amphibia and most of the 

 Eeptiles devoid of a pecten. B. Choroidal supply. This is probably 

 the chief supply of the retina in those animals which possess a well- 

 developed pecten (most Sauropsida), but are devoid of superficial 

 hyaloid vessels. This choroidal supply by osmosis is also with cer- 

 tainty demonstrated in the Mammalia for at least part of the thickness 

 of the retina. 



2. Direct supply. A. From the superficial hyaloid vessels. This is 



