I.] THE FROG. 143 



punctated appearance. It remains unstained 

 under the above method of treatment. 



e. The inner nuclear layer; nearly as thick as d., 

 and deeply stained. It is made up of a number 

 of nuclei, around each of which is collected a 

 very small amount of protoplasm ; and of fine 

 fibres, some of which can be traced into the same. 



f. The outer molecular (fenestrated} layer. Narrow 

 and unstained, somewhat resembling d. 



g. The outer nuclear layer. Much thinner than 

 the inner nuclear layer and more closely packed. 

 It is composed of distinct fibres (rod- and cone- 

 fibres), each of which swells out and has a 



nucleus developed in the enlargement. 

 h. The external limiting membrane. A thin homo- 

 geneous layer like a, obvious as a hard line 

 which not unfrequently overhangs the outer 

 nuclear layer. 

 /. 77ie rod- and cone-layer. Usually stained a faint 



pink colour under the above treatment, 

 a. The rods ; parallel and ending in blunted free 

 ends; each subdivided transversely into two 

 segments. 



ft. The cones ; few in number and shorter than 

 the rods; each ending in a pointed free end. 

 Look for them among the bases of the rods. 

 k. The pigment layer; seen to consist of a close set 

 series of elongated cells (pigment epithelium) 

 forming a cap-like investment for the free ends 

 of the rods and cones. 



a. The cell bases ; closely applied, each contain- 

 ing a round or oval clear nucleus. 



