Sorensen, Study of Epiphysis and Roof of Dienccphalon. 5 3 



tive cells of the organ. Their form in general is similar to those 

 of young Ammoccetes. The superior part of the rods is a lit- 

 tle thickened. In the inferior part is placed the nucleus, above 

 which the cell is prolonged and is transformed into a nervous 

 filament which passes across the inferior layers and grows into 

 the layer of nerve filaments. This prolongation does not unite 

 with other cells. Among these sensitive cells (batonnets) we 

 find cells with oval nuclei which are not colored. These have 

 no connection with the nerves. They are considered to be nu- 

 tritive cells for the retina. The superior end of these cells 

 turned toward the opening of the organ is bounded by a dis- 

 tinct line, above which our author believes that he finds vibratile 

 cilia. This might, however, be a sort of coagulum of the liquid 

 of the organ. There would be nothing extraordinary in the 

 former conception, since all the retina has the same origin as the 

 ependyma of the cerebro-spinal cavity, which has ordinarily a 

 ciliated epithelium. The composition of the retina just de- 

 scribed is uniform throughout. The rods are everywhere crowd- 

 ed and it is a very important fact that on the two sides of the 

 entrance of the canal into the cavity of the organ the nervous 

 prolongations of the rods are sometimes closely approximated. 

 It seems that these rods unite in fascicles. On the sides and in 

 the atrium the rods disappear. The thin vesicular wall is com- 

 posed of cylindrical and round nutritive ceils. Beyond this the 

 walls are composed of indistinct cells. These slightly resemble 

 the cells of the retina. Above the cylindrical cells a layer of 

 nervous filaments is found traversing the atrium longitudinally 

 and going from the nerve into the retina. 



The cell structure in adult Petromyzon differs much from that 

 in Ammoccetes. All of the cells of the layer of cylindrical cells 

 are of the same form and these sensitive cells are like those in Am- 

 moccetes. The other layers are similar throughout. Among 

 the basic cells incontestable ganglionic cells were found. The 

 difference between the retina of larvae and adult fishes has not 

 been recognized hitherto. The examination of the pineal organ 

 in adults presents much more difficulty than in Ammoccetes by 

 reason of the greater development of the pigment. At the ex- 



