88 



FREDERICK TILNEY AND LUTHER F. WARREN 



in which there were several layers of cells, including rod- and 

 cylindrical-shaped cells measuring from 7.4 to 8.3 micra in 

 diameter. There were also some larger cells scattered among 

 the rod cells with a mean diameter of 14 micra. He found in 

 the retina many nerve fibers which made their way into a definite 

 fasciculus constituting a parapineal nerve. Studnicka 388 did 

 not agree wholly with Owsiannikow in the idea that the para- 

 pineal end-vesicle was as well developed as the corresponding 

 structure of the pineal organ. He states that the difference 

 between these two structures is the fact that the parapineal 



Pell 



Ret 



Fig. 48 Sagittal section of the pineal and parapineal organs in Ammocoetes 

 with silver impregnation, according to Retzius, 1895. 



Ls., lamina terminalis; P/., paraphysis; Pp., parapineal organ; Ha., habenular 

 ganglion; Ret., retina; Pell., pellucida; N .pin., pineal nerve. 



end-vesicle is not as highly developed a retinal structure as is 

 the case with the pineal end-vesicle. Studnicka, however, finds 

 that there is in the dorsal wall of the parapineal vesicle a definite 

 pellucida made up of several layers of cells. Those cells iden- 

 tified in the retinal layer by Owsiannikow 295 and Studnicka 388 

 -as the rod cells were recognized by Retzius 331B in 1895 by means 

 of the Golgi method as bipolar cells. 



By this method Retzius 3313 was able to trace nerve fibers which 

 took origin in the left habenular ganglion and passed to the 

 parapineal end -vesicle. Leydig 239 in Petromyzon fiuviatilis 

 found that the parapineal end-vesicle was less developed, but at 



