THE EYE. 257 



surrounded by a single circle of rods (2). The further out- 

 wards we proceed, the further we find the cones removed 

 from each other, and the greater the number of rods situated 

 between them (3). 



Apes, andv the most of our domestic animals, present an 

 analogous condition. Nocturnal animals, such as the cat, 

 have only stunted cones ; bats, hedgehogs, moles, are entirely 

 deprived of the latter elements. Birds, on the contrary, 

 generally have an abundance of cones. In the chameleon 

 and lizard there are no rods at all ; we find only cones, as 

 in the human macula lutea. The rod appears to be the ter- 

 minal apparatus, serving for the objective colorless vision, as 

 the cone does for the color perception of the outer world 

 (Schultze). 



The membrana limitans externa, the sieve-like fenestrated 

 boundary structure, we are already familiar with. The rod 

 apices pass downwards through small spaces, the cone gran- 

 ules through larger ones. Finally, this membrane sends out- 

 wards the already mentioned delicate homogeneous connect- 

 ing substance between the rods and cones. 



The external granular layer, stratum granulosum externum, 

 is already familiar to us so far as its connective-tissue frame- 

 work is concerned. It (Fig. 203, B) consists of layers of 

 small cells stratified over each other, a minimal body closely 

 surrounding the nucleus. We distinguish here the larger 

 higher cone granules (c'), measuring 0.009 to O.012 mm., and 

 the smaller rod granules, measuring 0.0045 to 0.0079 mm., 

 situated more deeply. The latter alone present a peculiar, 

 perhaps normal transverse striation (Fig. 204, 4). 



Thus far the connection of the retinal elements is clear. 

 Now, however, on coming to the so-called intergranular 

 layer, the stratum intergranulosum, this clearness is lost. 

 There exists here a grievous defect of knowledge. 



Schultze, the excellent investigator whom we have thus far 

 followed, asserted that the finest rod-fibrillai, having arrived 

 at the intergranular stratum, formed very fine terminal knobs 

 (Fig. 203, B, above d). This is decidedly not the case. The 



