82 



FREDERICK TILNEY AND LUTHER F. WARREN 



fibroid, hyaline substance attached to the free end of the cells in 

 the retina. This took on the form of a coagulum in the semifluid 

 contents of the atrium. Later Studnicka 388 in 1899 described in 

 Petromyzon marinus similar hyaline bodies and showed that they 

 were the thickened extremities of the retinal cells projecting into 

 the lumen of the end- vesicle. 



^ f <^~r^'T^TT :r ?~r^^ 



\ 



Pell- -i'\W 



pp 



Fig. 46 Sagittal section of the epiphyseal complex of Petromyzon flaviatilis 

 showing syncytial masses in the Atrium, according to Studnicka, 1899. 

 Pell., pellucida; Po., pineal organ; Ret., retina; Pp., parapineal organ. 



In this way these processes from the retinal cells formed a 

 virtual syncytium which almost completely fills the atrium. Of 

 the two walls forming the end-vesicle, the ventral wall presents 

 certain characteristics which seem to justify the recognition in 

 it of a retinal structure. For this reason the ventral wall is 

 known as the retina of the pineal organ in cyclostomes. The 

 dorsal wall has an entirely different structural character, and 

 because it is quite without pigmentation is known as the pellucida. 



