THE PINEAL SYSTEM OF FISHES 



219 



fibres have been described ; also in some cases there is a definite nerve- 

 tract ending in the posterior commissure, and in embryos of Clupea 

 Holt has demonstrated nerve-fibres entering the habenular commissure. 



According to Galeotti some of the cells in the pineal organ of the so- 

 called white fish Leuciscus show indications of a secretory function, some 

 of the nuclei containing special fuchsinophile granules and secretory 

 products being found by him in the lumen of the organ. According to 

 Holt, however, the lumen of the organ contains only plasmatic strands con- 

 necting the opposite sides of the walls, or a delicate syncytium (Clupea). 



,MB. 



Hem 



Fig. 153. — The Pineal Organ of Ophidium barbatum, allied to the Blind 

 Deep-sea Fish Typhlonus. It is remarkable for the Great Length of 

 the Stalk and Insignificant Size of the End Vesicle. (After Studnicka.) 



Hem. : hemisphere. 

 MB. : midbrain. 

 olf. : olfactory nerve. 



po. : pineal organ. 

 r. sk. : roof of skull. 

 st. : stalk. 



ves 



-rium 



Fig. 154. — Longitudinal Section through a Single Tube of the Pineal 

 Organ of a Gar-pike (Belone acus), showing Knob-shaped Projections 

 into the Lumen of the Tube. These resemble the Refractile-knobs 

 which are present in the sensory vesicle of petromyzon, and were 

 considered by studnicka not to be secretory. the cells are ependymal 

 in Origin, and the Large Multipolar Cells beneath the External 

 Limiting Membrane resemble Ganglion Cells. (After Studnicka.) 



bl. corp. : blood corpuscles ; bl. ves. : blood vessel ; lum. : lumen. 



