78 W. J. DAKIX. 



nuclei of tliese cells had been seen before and they were 

 thought to lie inside the rod-cells. 



Kawitz agreed with Patten in almost all respects, but made 

 a retrograde step in asserting that a division of the outer 

 cells into three types was unnecessary because "die gesatnten 

 Zellen dieser Schicht vollstjlndig einander gleichen, abgesehen 

 natlirlicli von den nebensachlichen Differenzen im iiusseren 

 Habitus, und weil sie, vielfach miteinander in dii-ekter Kom- 

 munikation stehend, eine physiologische Einheit reprasen- 

 tieren." Schreiner also refers to the two layers of ganglionic 

 cells (the outer being a mixed layer, see table, and the inner 

 one the non-nervous inner interstitial cells), and states that 

 the outer layer is four or five cells deep in the middle of the 

 retina. He noticed, however, that the cells of the outermost 

 row (Piitten's first type) diffei-ed from tlie othei's, though 

 considers that all are of the same physiological nature. 

 Hesse in 1001 (34) was the first to upset the prevalent ideas 

 of these cells. He stated that there was only a single layer 

 of cells, and that the fibres of the distal nerve were not con- 

 nected with them. Hesse had forgotten, however, that the 

 previous observers would also have considered the outer 

 ganglionic layer to be of but one layer of cells if they had 

 only meant it to include the cells of Patten's first type. The 

 other cells Hesse alludes to as being pushed in between those 

 of the outer row, which he states are of epithelial-like nature. 

 In any case, to Hesse belongs the credit of having separated 

 off the outer interstitial cells from those of the most distal 

 layer, and breaking up the idea that all were ganglion-cells 

 and alike in function. 



In addition to the difference in shape and the fact that the 

 outer cells bear cilia-like processes (PI. 7, fig. 13, D. S.), he 

 also noticed that the nuclei of the outer cells were somewhat 

 different from those of the others, now termed " Zwischeu- 

 zellen." This difference has often been very apparent to me, 

 and it is strange that the earlier writers missed this point 

 unless fixation and staining of these cells had been rather 

 indifferent. 



