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. 



/ 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. 

 //. The external limiting membrane. A thin homo- 

 geneous layer like a, obvious as a hard line 

 which not unfrequently overhangs the outer 

 nuclear layer. 

 /. The 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. 



/?. 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. '^\VQ 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. 



