294 THE KETINA, BY MAX SCHULTZE. 



increases considerably, whilst the posterior remains unchanged.* 

 The former consists, on the fifth day of incubation, of very 

 numerous small fusiform cells, arranged vertically to the sur- 

 face ; the latter of a single layer of short prismatic cells con- 

 taining dark pigment. Remak was disposed, in consequence, 

 to recognize in these the first rudiment of the choroid, as 

 well as of the retina. By Kolliker/f 1 however, and more 

 recent inquirers,^: it has been demonstrated that the deve- 

 lopment of the pigmented connective tissue and of the ves- 

 sels of the choroid proceeds independently of the pigmented 

 layer of the primary eye vesicle. The posterior lamina of 

 the latter goes exclusively to form the pigment epithelium 

 of the retina, whilst the anterior lamina forms the remaining 

 layers of this membrane. The rods and cones are the last 

 to appear. Prior to their development the embryonal retina 

 is very sharply defined towards the pigmented epithelium 

 by a limitans externa. This "is much more distinct than 

 the limitans interna at the same period of development. It 

 corresponds in regard to its position, lining as it does the 

 cavity of the primary eye vesicle to the inner surface of the 

 cerebral ventricle, which in embryoes of the same age I find 

 to be lined by an equally sharply defined membrane. It ori- 

 ginates from a conical expansion of fibrils and fusiform cells 

 arranged vertically to the surface, the truncated extremities of 

 which lie in one plane, and are intimately attached to one 

 another to form a membrane. There is thus a complete simi- 

 larity of structure between the retina and the cerebral ventricles. 

 At this period no epithelial investment exists in either place. 

 From the seventh to the tenth day of incubation in Chickens, 



* See Remak, Entwickelung der Wirbelthiere, p. 35, Taf. v., fig 60 ; 

 Hensen, Virchow's Archiv, Band xxx., p. 181 ; and my detailed account 

 of the development of the retina in the Chick, Archiv fur Mikroskop. 

 Anatomie, Band ii., p. 239, Taf. viii. 



f Entwickelungsgeschichte der Wirbelthiere, p. 288, 1861, for Mammals. 



* Babuchin, Wurzburg not. Zeitschrift, Band iv., p. 71, 1863, for Mam- 

 mals, the Chick, and Frog ; Max Schultze in idem, for the Chick and for 

 Mammals ; Schenk, Sitzungsberichte der Akad. zu Wien, 1867 ; April part, 

 for Fishes. See also Hensen, Archiv fur Mikroskop. Anatomie, Band ii , p. 

 421. 



Max Schultze, Archiv fur Mikroskop. Anatomie, Band ii., p. 265. 



