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BLIND VERTEBRATES AND THEIR EYES. 



to 40 mm. in length the clinroid fissure is a well-marked structure. The pigment 

 layer and inner lasers merge into each other here, and the ganglionic layer is con- 

 tinuous with the pigment layer. As stated above, the inner reticular layer does not 

 surround the ganglionic layer at this point. A vertical longitudinal section of the 

 eye has the general appearance of a section through a Graafian follicle (fig. 41 a). 

 The ovum would correspond in position to a cell in the ganglionic layer, the stalk 



^^^?%.'"- 



I'IG. 42. (a) Verlic:il Seclion through Left Eye of Individual 2=; tnni. lonR. 



(b) Vertiral Section through Left Eye of Specimen 40 mm. long. Inner Layer of Cells of 

 Uvea shows well as a Series of Elongated Nuclei, til. I. Section, wfiile passing 

 through Ganglionic Layer, does not pass through i'upil. 



of the ovum to the lips of the fused choroidal fissure, the outer follicular cells to 

 the nuclear layers, antl the interior cavity of the follicle to the inner reticular layer 

 of the eye. 



Optic Nerve. — The optic nerve is not as distinct at its exit from the ganglionic 

 layer as in Amhlyopsis, but in specimens even 40 mm. long there is no difficulty 

 in tracing it to the brain. In specimens of the latter size it has a diameter of g /x. 

 It contains many elongated nuclei, some of which are also seen with the optic fibers 

 within the eye (fig. 42 h). The covering of the optic nerve partakes of the same 



