98 W. J. DAKIN. 



they are i-onnd and contain a conspicuous nucleolus together 

 with scattered chromatin granules. 



The cells of the pigment-layer appear to be continuous 

 with the retinal cells at the periphery of the retina. Patten 

 considered this layer, in fact, to be homologous with his outer 

 ganglionic layer. I am unable to say whether it should be 

 considered as a modified continuation of the distal sense-cells 

 or of the outer interstitial cells. The nuclei are much more 

 like those of the former, but the development of the Pecten 

 eye still requires elucidation. This completes the account of 

 the structures enclosed in the optic vesicle. A reference 

 must be made here to the inner wall of the proximal hemi- 

 sphere of the latter. It is formed of connective tissue, and 

 Patten called the surface layer the "sclerotica" (PI. 6, 

 fig. 1, 8c.). He described it as a two-layered, tough, hyaline, 

 connective-tissue membrane continuous with the septum. 



Rawitz disagreed entirely with this and objected to the 

 term "sclerotica," because of its inappropriateness, considering 

 the use of this term in the nomenclature of the vei'tebrate 

 eye. This membrane of Patten is, however, well marked in 

 longitudinal sections of the eye, though it is simply the 

 limiting or surface layer of the connective tissue of the eye- 

 stalk and directly continuous with it. In sections stained 

 with Mallory's fluid it is very conspicuous (PI. 6, fig. 1, Sc), 

 and stains a deep blue against the light blue of the ground 

 tissue of the eye-stalk. It also differs from the latter in 

 being hyaline and containing neither fibrous elements nor 

 nuclei. The connective tissue forming the wall of the distal 

 part of the optic vesicle lacks this differentiated surface layer 

 entirely. In reactions to several stains it resembles the 

 septum, and it also appears to be continuous with this mem- 

 brane. The layer is thus obvious, but is not to be considered 

 as a separate structure in Patten's sense, and the term 

 "sclerotica" is certainly inapplicable. 



I have called it simply " the modified connective tissue-wall 

 of the optic vesicle." It must be remembered that the terms 

 "cornea," "sclerotica," "iris," etc., used by Patten and others 



